Anodized die cast aluminum alloy and method of making and using same

Abstract

The application discloses anodized pressure-cast aluminum alloy and a preparation method and application thereof, and belongs to the technical field of pressure casting molding. The aluminum alloy contains 0.3-1.0% of Si, 0.4-1.5% of Mg, 0.01-0.2% of Ti and ≤0.3% of impurities in mass percentage, and the rest is Al; the average grain size of the pressure-cast state is 10-30 μm (standard deviation ≤30 μm), and there is not more than 1 pore with an area of ≥10 μm 2 in any 500 μm 2 square region; the application breaks the process bottleneck of low-silicon 6-series aluminum alloy which is difficult to complete the pressure casting due to the limited melt fluidity, and makes the manufacturing of high-end anodized structural parts get rid of the dependence on traditional rolling / forging plates and CNC machining paths, realizes extremely low anodized color difference while keeping good mechanical properties, effectively eliminates appearance defects such as flow lines, black lines and glares, has low surface defect occurrence rate, and has appearance quality close to that of rolling plates.

Description

Technical Field

[0001] This invention belongs to the field of die casting technology, specifically relating to an anodized die-cast aluminum alloy, its preparation method, and its application. Background Technology

[0002] Aluminum alloy die casting, as a highly efficient and near-net-shape metal parts manufacturing process, has been widely used in high-end manufacturing fields such as consumer electronics casings, automotive structural parts, and robotic mechanical components due to its advantages such as high production efficiency and the ability to form complex structures. In these applications, the appearance quality and mechanical properties of the product are often equally important. Especially for high-end consumer electronics products, anodizing has become a key process in aluminum alloy surface treatment. By forming a dense alumina film on the aluminum alloy surface, not only is the product endowed with excellent wear resistance and corrosion resistance, but it can also achieve rich and uniform decorative coloring effects. However, the quality of the anodized film is highly dependent on the purity of the matrix material and the uniformity of its microstructure. Any microscale component segregation, porosity defects, or uneven distribution of the second phase will be significantly amplified during the electrochemical oxidation process, manifesting as visible appearance defects such as color difference, flow lines, black streaks, or glitter.

[0003] 6-series aluminum alloys (Al-Mg-Si series, such as 6061 and 6063), as representatives of medium-to-high strength aluminum alloys, can achieve good comprehensive mechanical properties and excellent corrosion resistance through aging to precipitate the Mg2Si strengthening phase, making them widely used in structurally integrated components. However, 6-series aluminum alloys still face technical bottlenecks in die casting and anodizing. Specifically, to obtain good die casting fluidity and avoid defects such as cold shuts and undercasting, traditional die casting processes tend to increase the silicon content; however, silicon has a significant negative impact on anodizing performance. During anodizing, the silicon phase is difficult to participate in the formation of the alumina film, leading to a significant increase in local porosity of the film layer, and the appearance of obvious color differences and uneven coloring on the surface. More seriously, silicon reacts chemically with sulfuric acid anodizing solution to generate insoluble silicate precipitates, which not only contaminate the electrolyte and reduce its conductivity, but also form difficult-to-remove residues on the oxide film surface, resulting in a dull oxide film color and poor uniformity. Therefore, it is currently difficult to simultaneously achieve good die casting performance and anodizing performance in 6-series aluminum alloys.

[0004] On the other hand, the rapid solidification characteristic unique to die casting further exacerbates the difficulty of microstructure control in 6-series aluminum alloys. Under high-speed cooling conditions, alloying elements such as Mg and Si in the melt are prone to segregation at grain boundaries, forming coarse or unevenly distributed Mg2Si secondary phases. At the same time, the uneven dendritic structure and locally enriched strengthening phases will lead to inconsistent oxide film growth rates during subsequent anodizing due to differences in electrochemical activity in micro-regions, resulting in macroscopic surface defects such as flow lines and black streaks.

[0005] Current technologies have not effectively solved the problem of synergistic control of die-casting formability and microstructure uniformity of 6-series aluminum alloys under low-silicon conditions. Therefore, there is an urgent need to develop a 6-series low-silicon die-casting aluminum alloy that combines good mechanical properties, excellent die-casting formability, and high-quality anodized appearance.

[0006] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0007] This invention provides an anodized die-cast aluminum alloy, its preparation method, and its application, at least solving the technical problem that existing 6-series aluminum alloys cannot simultaneously possess high mechanical properties, good die-casting formability, and excellent anodizing performance. Furthermore, it also addresses the long-standing technical issue that high-end anodized exterior parts made from low-silicon 6-series aluminum alloys have relied on sheet metal machining.

[0008] To achieve the above objectives, in a first aspect, the present invention provides an anodized die-cast aluminum alloy, wherein, by mass percentage, the anodized die-cast aluminum alloy comprises the following elements: 0.3% to 1.0% Si, 0.4% to 1.5% Mg, the total content of unavoidable impurities not exceeding 0.3%, and the balance being Al; Before heat treatment, the average grain size of aluminum alloy is 10μm~30μm, and the standard deviation of the grain size is no greater than 30μm; in any 500μm of aluminum alloy 2 Within the observation area, the area is not less than 10 μm 2 The number of pores is no more than 1.

[0009] Preferably, before heat treatment, the aluminum alloy is subjected to heat treatment on any 500μm section. 2 Within the observation area, there is no area not less than 10 μm 2 pores.

[0010] Preferably, before heat treatment, the solid solution concentration of Mg at the grain boundaries of the aluminum alloy varies in a banded pattern with a width of more than 0.1 mm along the width direction of the alloy, and the concentration difference between adjacent bands is less than 0.15% by mass.

[0011] Preferably, after heat treatment, the aluminum alloy contains two Mg2Si intermetallic compounds, F and G, wherein the equivalent circle diameter of intermetallic compound F is 3μm~6μm and the equivalent circle diameter of intermetallic compound G is 0.03μm~3μm; in any observation region of the aluminum alloy, the ratio (f / g) of the area ratio f of intermetallic compound F to the area ratio g of intermetallic compound G is 1.5~4.

[0012] Preferably, in any observation area of ​​the aluminum alloy, the sum of the area ratio f of intermetallic compound F and the area ratio g of intermetallic compound G is not less than 1.5%.

[0013] Preferably, the intermetallic compound F is in a continuous network morphology, and the intermetallic compound G is in a needle-like morphology.

[0014] Preferably, the dispersion density of the Mg2Si intermetallic compound is 10 particles / μm. 2 ~200 cells / μm 2 .

[0015] Preferably, after the aluminum alloy is anodized, its surface has an anodized film, and the arithmetic mean height Sa of the anodized film is 0.1μm~0.5μm, and the average width Rsm of the contour unit is 0.5μm~10μm.

[0016] Preferably, the surface color of the anodized die-cast aluminum alloy has a* < 0.1, b* < 1.0, and L* < 25.

[0017] Preferably, the incidence of surface defects in the anodic oxide film is less than 0.05%.

[0018] Preferably, the anodized die-cast aluminum alloy comprises 0.6% to 0.8% Si by mass percentage.

[0019] Preferably, the anodized die-cast aluminum alloy further comprises 0.01% to 0.2% Ti by mass percentage.

[0020] Preferably, the anodized die-cast aluminum alloy further comprises 0.1% to 0.15% Ti by mass percentage.

[0021] Preferably, the solidification point range of the anodized die-cast aluminum alloy is 570℃~620℃.

[0022] Preferably, the heat treatment includes T4, T5, T6 or T651 heat treatment.

[0023] In a second aspect, the present invention provides a method for preparing the anodized die-cast aluminum alloy of the first aspect, comprising the following steps: Step S102: After melting the metal alloy to form a molten liquid, the molten liquid includes the following elements by mass percentage: 0.3%~1.0% Si, 0.4%~1.5% Mg, the total content of unavoidable impurities is not greater than 0.3%, and the balance is Al; The molten liquid is kept at a first temperature, and the mold is kept at a second temperature lower than the first temperature. The temperature difference between the first and second temperatures is 300℃~350℃. Step S104: Inject the molten liquid into the mold cavity. After the mold cavity is filled, maintain pressure and open the mold to obtain the die-cast aluminum alloy. The speed at which the molten liquid is injected into the mold cavity shall not exceed 2 m / s, and the moving speed of the molten liquid surface relative to the mold cavity shall not exceed 0.5 m / s; The cross-sectional area of ​​the flow channel varies within ±10% between the position where the liquid inlet contacts the mold cavity and the position where it is far away from the mold cavity; The ratio between the overflow rate of the molten filling and the volume of the mold cavity shall not be less than 0.1; Step S106: Heat-treat and anodize the die-cast aluminum alloy to obtain anodized die-cast aluminum alloy.

[0024] Preferably, the ratio between the overflow of the melt filling and the volume of the mold cavity is in the range of 0.1 to 0.5.

[0025] Preferably, the overflow rate of the molten metal filling and the volume of the mold cavity satisfy the following relationship:

[0026] In the formula, Overflow volume for molten filling; This refers to the volume of the mold cavity; This is the first proportionality constant, and its value ranges from 0.1 to 0.2; The temperature difference between the first temperature and the second temperature. The second temperature; The speed at which molten liquid is injected into the mold cavity.

[0027] Preferably, the molten filling overflow is discharged through an overflow port on the mold cavity; the overflow port is circumferentially located on the side wall of the mold cavity, and the area of ​​the overflow port accounts for 15% to 25% of the surface area of ​​the side wall of the mold cavity.

[0028] Preferably, the heat treatment is T6 heat treatment, and the specific steps include: solution treatment at 520℃~540℃ for 1 hour to 4 hours, water quenching, and then aging treatment at 160℃~180℃ for 6 hours to 12 hours.

[0029] Preferably, the anodizing treatment includes: in a sulfuric acid electrolyte with a concentration of 150 g / L to 200 g / L, at a temperature of 18°C ​​to 22°C, at an anode flow rate of 1.0 A / dm³. 2 ~1.5A / dm 2 DC anodizing is performed at a current density of 20 to 40 minutes.

[0030] Thirdly, the present invention provides an aluminum alloy die casting made of an anodized die casting aluminum alloy of the first aspect, or an anodized die casting aluminum alloy prepared by the preparation method of the second aspect.

[0031] Fourthly, the present invention provides an application of the aluminum alloy die-casting part as described in the third aspect in the manufacture of structural parts for electronic devices, transportation vehicles, robots, medical devices, industrial equipment, or new energy equipment.

[0032] The beneficial effects of this invention are as follows: The anodized die-cast aluminum alloy provided by this invention, through the synergistic effect of precise low-silicon composition design and microstructure control, successfully enables 6-series aluminum alloys to simultaneously possess good mechanical properties, excellent die-casting formability, and high-quality anodizing performance. Traditional 6-series aluminum alloys (such as 6061 and 6063) still face technical bottlenecks in die-casting applications: while increasing silicon content to improve fluidity can alleviate forming defects such as cold shuts and undercasting, excessive silicon can severely interfere with the formation process of the alumina film. The silicon phase is difficult to participate in oxide film construction during anodizing, leading to a significant increase in local porosity of the film layer; simultaneously, silicon reacts with sulfuric acid electrolyte to form insoluble silicate precipitates, which not only contaminate the electrolyte and reduce its conductivity but also form difficult-to-remove residues on the oxide film surface, ultimately resulting in a dull oxide film color, significant color difference, and uneven color defects. This invention controls the silicon content within an optimized range of 0.3% to 1.0%. While ensuring the silicon source required to form a sufficient amount of Mg2Si strengthening phase, it weakens the destructive impact of silicon on the quality of the anodic oxide film from the source of composition. This enables 6-series aluminum alloys to maintain high strength characteristics while achieving the feasibility of high-quality anodizing of die-cast parts. After anodizing, the color difference is extremely low, and there are no macroscopic defects such as watermarks, black lines, and glitter on the surface. The appearance quality reaches or even approaches the level of rolled sheet metal.

[0033] Furthermore, this invention significantly optimizes the solidification behavior and grain refinement of the alloy through the synergistic design of low silicon and magnesium content, supplemented by the addition of trace amounts of titanium. Titanium, as an effective grain refiner, can form high-melting-point Al3Ti heterogeneous nucleation cores with aluminum, providing numerous nucleation sites in the early stages of melt solidification and effectively inhibiting abnormal grain growth. Simultaneously, the addition of titanium, in conjunction with 0.3%–1.0% silicon and 0.4%–1.5% magnesium content, rationally controls the solidification temperature range of the alloy, effectively widening the mushy region and significantly reducing the tendency for hot cracking. Combined with the strategies of controlling the temperature difference between the melt and the mold, slow filling, and large overflow in the die-casting process, the growth rate of the edge cooling layer can be controlled, avoiding dendrite coarsening and magnesium segregation caused by rapid cooling in traditional die casting. The resulting die-cast microstructure exhibits highly uniform fine-grained characteristics and extremely high internal density, fundamentally suppressing the formation of macroscopic defects. Furthermore, the magnesium solid solution concentration at the grain boundaries exhibits uniformity at the microscale, effectively preventing appearance defects caused by local electrochemical activity differences during the anodizing process.

[0034] Furthermore, after heat treatment, the Mg2Si strengthening phase precipitated in the alloy of this invention exhibits a unique dual-morphological distribution characteristic. This specific morphology and distribution of the strengthening phase structure, on the one hand, provides good strength support and grain boundary pinning through the continuous network of intermetallic compounds F, and on the other hand, achieves efficient precipitation strengthening through fine and dispersed intermetallic compounds G, jointly ensuring the mechanical properties of the alloy. At the same time, the controlled network structure avoids the formation of local current concentration points during the anodizing process, and the fine intermetallic compounds G are moderately retained and uniformly embedded in the alumina matrix during the oxidation process, forming an optimized surface micromorphology. This not only does not destroy the continuity of the film layer, but also optimizes the surface optical properties by controlling the light scattering behavior, ultimately obtaining a high-quality oxide film without the formation of striped textures or scintillation defects on the surface, meeting the stringent requirements of high-end consumer electronics products for visible defects.

[0035] To achieve a balance between mechanical properties and aesthetic quality in 6-series aluminum alloys, this invention provides a preferred process co-control system. This system enables the stable production of 6-series aluminum alloy structural parts suitable for high-end anodizing using die casting, a highly efficient, near-net-shape forming process. It overcomes the traditional bottleneck of low-silicon 6-series aluminum alloys, which are difficult to fully fill and form due to limited melt flowability, achieving high-yield, complete forming of low-silicon die-cast aluminum alloys. This technical solution frees the production of high-end anodized parts from dependence on traditional rolled / forged sheet metal and CNC machining. By directly using die-cast blanks for heat treatment and anodizing, the appearance yield and dimensional accuracy can be achieved close to those of sheet metal machined parts, effectively solving the long-standing technical bottleneck of balancing die-casting formability and anodizing performance in 6-series aluminum alloys. This technological breakthrough provides a cost-effective and performance-advantageous manufacturing solution for thin and light structural parts such as mobile phone frames and laptop casings, potentially replacing some forged or rolled 6-series aluminum alloy parts that require CNC precision machining. It significantly reduces material and processing costs while maintaining a high-end product feel, possessing significant industrial value and market potential. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 The image shows the metallographic structure of the aluminum alloy sample after T6 heat treatment in Example 1 of this invention. Figure 2 The image shows the metallographic structure of the aluminum alloy in the die-cast state in Embodiment 1 of the present invention; Figure 3 The image shows the metallographic structure of the aluminum alloy sample after T6 heat treatment in Example 11 of this invention. Figure 4 The image shows the metallographic structure of the aluminum alloy in the die-cast state in Embodiment 11 of the present invention. Figure 5 This is a photograph of the appearance of an aluminum alloy die-casting part made of aluminum alloy after anodizing, as shown in Embodiment 1 of the present invention. Figure 6 This is a photograph of the appearance of the aluminum alloy die casting made of aluminum alloy in Comparative Example 2 of the present invention after anodizing. Figure 7 This is a schematic diagram of the gateless structure provided in Embodiment 1 of the present invention; Figure 8 This is a schematic diagram of the narrow gate structure provided in Comparative Example 4 of the present invention; Figure 9This is a three-dimensional structural diagram of the mold provided in Embodiment 1 of the present invention; Figure 10 This is a side view of the mold provided in Embodiment 1 of the present invention.

[0038] Explanation of reference numerals in the attached figures: 10. Mold cavity; 20. Liquid inlet; 30. Overflow outlet; 40. Injection mechanism. Detailed Implementation

[0039] In this invention, unless otherwise stated, directional terms such as "up," "down," "left," and "right" are generally understood in conjunction with the accompanying drawings and the directions shown in actual applications.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0041] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0042] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0043] To achieve the above objectives, in a first aspect, the present invention provides an anodized die-cast aluminum alloy, wherein, by mass percentage, the anodized die-cast aluminum alloy comprises the following elements: 0.3% to 1.0% Si, which can be 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1.0%, and any value between therewith. Preferably, by mass percentage, the anodized die-cast aluminum alloy comprises 0.6% to 0.8% Si.

[0044] The Mg content can be 0.4% to 1.5%, and can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any value between them.

[0045] The total content of unavoidable impurities shall not exceed 0.3%, and may be 0.3%, 0.25%, 0.2%, 0.15%, 0.1%, 0.05%, lower, or any value between them, with the balance being Al.

[0046] Preferably, the anodized die-cast aluminum alloy further comprises 0.01% to 0.2% Ti by mass percentage, which can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, and any value between them. More preferably, the anodized die-cast aluminum alloy further comprises 0.1% to 0.15% Ti by mass percentage.

[0047] The above-described composition design helps this invention resolve the contradiction between die-casting and anodizing performance of 6-series aluminum alloys. Compared to traditional 6-series die-cast aluminum alloys, this invention actively and significantly reduces the Si content. Traditional 6-series die-cast aluminum alloys typically have a high Si content (e.g., above 1.0%, even exceeding 4%) to achieve good fluidity and avoid defects such as cold shuts and undercasting. However, high silicon content has a significant negative impact on anodizing performance. During anodizing, the silicon phase (such as eutectic silicon or primary silicon) acts as an electrochemically inert phase and cannot effectively participate in the formation of the alumina film. The presence of the silicon phase hinders the continuous and uniform growth of the alumina film, resulting in a loose structure and abnormally high porosity in this region. More seriously, silicon reacts with sulfate ions in the sulfuric acid anodizing electrolyte to form insoluble silicate (such as aluminum silicate) precipitates or colloids. These silicate products can adhere to the surface of the oxide film or clog its pores, leading to decreased film gloss, dull color, white spots, or a cloudy appearance, and significantly reducing the corrosion resistance and color uniformity of the oxide film. Furthermore, the difference in dissolution rates between the silicon phase and the aluminum matrix during the anodizing process causes uneven distribution of microscopic current density, which is one of the root causes of macroscopic defects such as color differences between the positive and negative surfaces, flow lines, and black streaks. Therefore, this invention limits the Si content to a low level range of 0.3% to 1.0%, aiming to reduce the negative impact of silicon on the quality of the anodized film from the source, while ensuring the formation of a sufficient amount of Mg2Si reinforcing phase to provide the required strength, thus ensuring a highly uniform, high-gloss, and color-difference-free anodized surface.

[0048] Furthermore, optimizing the Si content to be within the range of 0.5% to 0.8% helps to achieve a balance between mechanical properties and anodizing performance. When the Si content is below 0.3%, there is insufficient silicon source to form the strengthening phase Mg2Si. Even if the Mg content is sufficient, the total amount of Mg2Si phase precipitated after aging treatment may not be enough to provide the desired strength level of the 6-series aluminum alloy, resulting in substandard mechanical properties (especially yield strength). At the same time, excessively low Si content will increase the liquidus temperature of the alloy, narrow the solidification range, potentially increase the tendency for hot cracking during die casting, and reduce melt fluidity, which is not conducive to filling complex thin-walled parts. When the Si content is above 1.0%, although it is beneficial to improve fluidity and the formation of the Mg2Si phase, excess free silicon or silicon phase existing in the form of coarse eutectic silicon will drastically deteriorate the anodizing performance. The aforementioned silicon interference effect will become significant, leading to a serious decline in oxide film quality and making it difficult to meet high-end appearance requirements. Therefore, by controlling the Si content to 0.3% to 1.0%, preferably 0.5% to 0.8%, it is possible to maintain the necessary strength and good formability while keeping the harmful effects of silicon on anodizing within an acceptable range.

[0049] In the composition system of this invention, Mg is another important alloying element, mainly combining with Si to form the Mg2Si strengthening phase. Its content range is set at 0.4% to 1.5%, intended to synergistically match the aforementioned Si content range. If the Mg content is too low, even with sufficient Si content, a adequate amount of Mg2Si phase cannot be formed, resulting in insufficient age-hardening and low strength. If the Mg content is too high, although it may increase strength, excessive Mg may form other brittle phases (such as Al3Mg2), impairing the alloy's plasticity and toughness. Simultaneously, under rapid solidification conditions during die casting, excessive Mg easily leads to severe segregation at grain boundaries, forming coarse or discontinuous Mg2Si phases or Mg-rich phases. This microscopic compositional inhomogeneity transforms into macroscopic electrochemical inhomogeneity during anodizing, resulting in uneven oxide film thickness and color differences. Therefore, controlling the Mg content at 0.4% to 1.5%, and matching it with the low-silicon design, aims to obtain a moderately and uniformly distributed Mg2Si strengthening phase, thereby balancing mechanical properties and the matrix uniformity required for anodizing.

[0050] This invention preferably adds 0.01% to 0.2% Ti, more preferably 0.1% to 0.15%. Ti is commonly used as a grain refiner in aluminum alloys. During die casting, the melt cools at an extremely rapid rate, easily forming coarse columnar or equiaxed crystals, making grain size difficult to control. The addition of Ti can form high-melting-point Al3Ti particles with Al. These particles act as heterogeneous nucleation nuclei in the early stages of melt solidification, effectively increasing the nucleation rate and thus significantly refining the solidification structure to obtain fine and uniform equiaxed crystals. For anodized die castings that require high appearance quality, a fine and uniform grain structure is crucial. Coarse grains lead to a reduction in grain boundaries, which are the preferred channels and weak points for the growth of anodized films. When grain size differences are too large or coarse grains are present, different grain orientations and grain boundary density regions respond differently to the oxidation current, resulting in uneven oxide film growth rate and thickness, manifested as macroscopic color differences, flow lines, or scintillation defects. Ti refines the grain structure, resulting in a fine-grained microstructure with uniform size and concentrated distribution, providing an ideal microstructure substrate for obtaining a uniform anodic oxide film. Simultaneously, the refined grains also contribute to improving the alloy's strength and plasticity. When the Ti content is too low, the refining effect is not significant; when it is too high, coarse primary Al3Ti phases may form, which can become stress concentration sources or disrupt matrix continuity, adversely affecting toughness and anodic oxide uniformity. Therefore, controlling the Ti content at 0.01%–0.2%, preferably 0.1%–0.15%, achieves effective grain refinement while avoiding the negative effects of excessive addition.

[0051] Unavoidable impurities mainly refer to elements such as Fe, Cu, Mn, and Cr. Fe readily forms hard and brittle needle-like or lamellar Fe-rich phases (such as Al3Fe and α-AlFeSi) with Al. These phases not only fracture the matrix and impair plasticity and toughness, but also, due to their large potential difference with the aluminum matrix during anodizing, become the cathode for micro-galvanic corrosion, leading to selective dissolution of the surrounding matrix and the formation of corrosion pits or dark spots under or on the surface of the oxide film. Although Cu can improve strength and hardness, it significantly reduces the corrosion resistance of the alloy, especially after anodizing, where Cu-rich areas may affect color uniformity. Therefore, this invention aims to maintain the purity and electrochemical homogeneity of the matrix by strictly controlling the total amount of impurities to ≤0.3%, which helps to obtain a high-quality anodic oxide film.

[0052] It should be noted that the anodized die-cast aluminum alloy provided by this invention can be stably subjected to standard strengthening heat treatments, including T4 (natural aging after solution treatment), T5 (artificial aging after casting cooling), T6 (complete artificial aging after solution treatment), or T651 (stress relief and artificial aging after solution treatment), all of which can yield anodized die-cast aluminum alloys that meet the requirements of this invention. However, more preferably, the anodized die-cast aluminum alloy of this invention can achieve relatively superior microstructure and performance results after T6 heat treatment. Therefore, in the following specific embodiments, the heat treatment of this invention is illustrated using T6 heat treatment.

[0053] Before T6 heat treatment, the average grain size of the aluminum alloy is 10μm to 30μm, which can be 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm and any value between them; the standard deviation of the grain size is not greater than 30μm, which can be 30μm, 25μm, 20μm, 15μm, 10μm, 5μm and any value between them.

[0054] Understandably, controlling the average grain size in the die-cast state within the range of 10μm to 30μm and the standard deviation of the grain size not greater than 30μm is the key microstructure basis for achieving synergistic optimization of the die-casting formability and anodizing performance of 6-series aluminum alloys in this invention.

[0055] Understandably, the "die-cast state" specifically refers to the original state of the alloy after demolding without any subsequent heat treatment, and its microstructure directly reflects the thermodynamic and kinetic behavior of the melt during solidification. In the 6-series aluminum alloy system, the silicon content is strictly controlled at a low level of 0.3% to 1.0%. While this significantly reduces the negative impact of silicon on the quality of the anodic oxide film, it also reduces the alloy's natural nucleation ability and narrows the solidification temperature range. Under this composition, the average grain size is limited to the range of 10 μm to 30 μm, which avoids the problems of excessively fine grains leading to excessively rapid solidification front advancement and increased microsegregation of solute elements (especially magnesium) at grain boundaries, while also preventing the amplification effect of crystallographic orientation differences caused by excessively coarse grains.

[0056] When the grain size is less than 10 μm, the excessively high nucleation rate causes the solidification process to be completed in a very short time. Solute elements such as magnesium and silicon do not have enough time to achieve uniform distribution through diffusion, forcing them to form a large concentration gradient in the grain boundary region. This microscopic compositional inhomogeneity translates into localized differences in electrochemical activity during anodizing, leading to abnormal growth rates of the oxide film near the grain boundaries. Macroscopically, this manifests as a network of color differences or flow-line defects distributed along the grain boundaries. When the grain size is greater than 30 μm, the surface energy differences between different orientation regions within the coarse grains are significant, forming micro-potential differences in the sulfuric acid electrolyte. This results in increased dispersion of the oxide film growth rate and an excessively large standard deviation in film thickness, ultimately exhibiting visible scintillation or striped texture under specific lighting angles. The grain size range of 10 μm to 30 μm allows 6-series aluminum alloys to still obtain a physically homogeneous matrix structure under low silicon conditions, providing a reaction interface with consistent electrochemical behavior for subsequent anodizing.

[0057] Furthermore, this invention limits the standard deviation of grain size to no more than 30 μm. This parameter setting takes into account the microstructure evolution characteristics of 6-series aluminum alloys under rapid solidification conditions during die casting. The standard deviation, as a statistical measure characterizing the degree of grain size dispersion, has the physical significance of quantifying the concentration of grain size distribution in the microstructure. When the standard deviation exceeds 30 μm, there will inevitably be both significantly smaller fine-grained regions and significantly larger coarse-grained regions in the microstructure, and their electrochemical behaviors during anodizing differ greatly. Specifically, the fine-grained regions, due to their high grain boundary density and relatively mild solute element segregation, exhibit a faster oxide film growth rate and a denser film structure; while the coarse-grained regions, due to their sparse grain boundaries and large internal orientation differences, exhibit a slower oxide film growth rate and significant film thickness fluctuations. This binary differentiation of growth rates forms a significant film thickness gradient at the boundary between fine and coarse grains. This gradient region produces non-uniform scattering of incident light, which appears macroscopically as striped, alternating light and dark texture defects.

[0058] It should be noted that 6-series aluminum alloys have a wider solidification temperature range and a more pronounced pasty region compared to 7-series alloys. This makes them less sensitive to fluctuations in cooling conditions during die casting, thus allowing for a relatively loose standard deviation control range (≤30μm). This range ensures the basic requirement of microstructure uniformity while also taking into account the process window adaptability for industrial production, avoiding the decrease in production yield and increase in cost caused by excessively small control standard deviation.

[0059] Optionally, the testing of grain size and its distribution is performed according to ASTM E112 standard. The specific method is as follows: cut a die-cast sample, mechanically grind and polish it, and then etch it with Keller's reagent. Observe the microstructure at least 5 different fields of view using a metallographic microscope at 500x magnification or a field emission scanning electron microscope. Automatically identify grain boundaries using image analysis software, calculate the equivalent circle diameter of each grain (i.e., the diameter of a circle with the same projected area as the grain), and calculate the arithmetic mean of all measured grains to obtain the average grain size. At the same time, calculate the standard deviation to characterize the dispersion of the size distribution.

[0060] In any 500μm of aluminum alloy 2 Within the observation area, the area is not less than 10 μm 2 The number of pores is no more than 1, and can be 0 or 1. More preferably, before the aluminum alloy undergoes T6 heat treatment, any 500μm of the aluminum alloy... 2 Within the observation area, there is no area not less than 10 μm 2 pores.

[0061] It should be noted that the "porosity" mentioned in this invention specifically refers to closed void defects formed inside the die-cast aluminum alloy due to gas entrapment or solidification shrinkage, including gas pores (formed by gas entrapment in the melt, with an approximately spherical morphology and a major axis / minor axis ratio <1.5) and shrinkage cavities (formed by insufficient feeding, with an irregular morphology and a major axis / minor axis ratio ≥1.5). The pore area was determined by observing cross-sectional samples after mechanical polishing and Keller's reagent etching using a metallographic microscope (500x magnification) or a field emission scanning electron microscope. Image analysis software was used to automatically identify the pore contours and calculate their projected areas. The observation area was set to 500 μm. 2 It can reflect the density of local tissues while avoiding statistical fluctuations caused by an excessively small observation area.

[0062] The silicon content of 6-series aluminum alloys is strictly controlled at a low level of 0.3% to 1.0%. While this significantly reduces the destructive impact of silicon on the quality of the anodized film, it also relatively reduces the fluidity of the melt, placing higher demands on the control of gas entrapment and feeding behavior in the die-casting process. Under low-silicon conditions, the surface tension of the melt increases, making it more difficult for bubbles to rise and escape; at the same time, the solidification temperature range is relatively narrowed, increasing the risk of premature closure of the feeding channels. Therefore, this invention sets the critical size of harmful porosity at 10 μm. 2 The observation area was set to 500 μm. 2 This ensures that high-density castings can still be obtained under conditions of relatively limited fluidity.

[0063] When the pore density exceeds 1 pore / 500μm 2 At this time, the incidence of surface defects (dark spots, bright spots, corrosion spots) will increase sharply after anodizing. The mechanism may include: First, the geometric curvature effect at the edge of the pores creates a local electric field concentration. The smaller the radius of curvature, the higher the current density, resulting in a significantly higher oxide film growth rate than in flat substrate areas. The film thickness exceeds the normal range, and the structure is loose and porous, macroscopically manifested as ring-shaped dark spots around the pores. Second, sulfuric acid electrolyte is easily retained inside the pores. During the washing and drying process after oxidation, the residual acid slowly seeps out and continues to corrode the newly formed oxide film, forming corrosion spots, which are particularly noticeable after dark coloring. Third, as a typical stress concentration source, the pores undergo volume expansion due to the conversion of aluminum to alumina during oxide film growth, which induces microcracks around the pores, destroying the continuity of the film layer and significantly reducing the corrosion resistance of the area, making it prone to becoming a corrosion initiation point in subsequent use environments.

[0064] Therefore, the present invention uses die-cast aluminum alloys with an area of ​​not less than 10 μm 2 The pore density is strictly controlled to be no more than 1 pore / 500 μm. 2 The level is preferably one where the area of ​​complete elimination is ≥10μm. 2 The pores are a key structure that ensures the high-quality anodized appearance of 6-series low-silicon die-cast aluminum alloys. They can significantly reduce the occurrence rate of surface defects after anodizing and stably control color difference. They are particularly suitable for consumer electronics products such as smartphone frames and tablet back panels that have extremely high requirements for surface quality.

[0065] Preferably, before the aluminum alloy undergoes T6 heat treatment, the solid solution concentration of Mg at the grain boundaries of the aluminum alloy varies in a stripe pattern along the width direction of the alloy with a width of 0.1 mm or more (which can be 0.1 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, or any value between them), and the concentration difference between adjacent stripes is less than 0.15% by mass, which can be 0.15%, 0.14%, 0.13%, 0.12%, 0.11%, 0.10%, or even lower, or any value between them.

[0066] This invention quantifies the uniformity of microstructure composition in die-cast 6-series aluminum alloys. The aim is to control the segregation of solute elements inherent in the rapid solidification process of die casting into a moderate and broad distribution pattern, rather than sharp and localized grain boundary enrichment, by defining the spatial structure and gradient intensity of the concentration distribution.

[0067] It should be clarified that the "banded variation" mentioned in this invention specifically refers to a macroscopic composition band formed by the arrangement and connection of multiple solute segregation regions at the grain boundaries along the width direction of the alloy. The macroscopic composition band has a width of more than 0.1 mm in the width direction of the alloy, and the solid solution concentration of Mg shows a continuous and gentle gradient change. The absolute difference between adjacent bands does not exceed 0.15 mass.

[0068] It should be noted that the above phenomena can be determined by line scanning analysis using electron probe microanalysis (EPMA) or a scanning electron microscope equipped with energy dispersive spectroscopy (EDS): On the polished and etched metallographic sample, a line scan with a length of not less than 0.3 mm is selected in a direction parallel to the width of the alloy and spanning multiple grains, with a step size set to 5 μm, to obtain the concentration distribution curve of Mg element; a continuous interval with a concentration change of less than 0.03% by mass is defined as a "band", the concentration jump value between adjacent bands is the concentration difference, and the projection length of the concentration change region in space is the band width.

[0069] In traditional aluminum alloy die casting, due to the excessively rapid cooling rate and narrow solidification range, Mg solute elements are largely repelled by the rapidly advancing solidification front to the grain boundary region where solidification occurs last, forming sharp enrichment peaks with narrow widths. These enriched grain boundaries are arranged perpendicular to the filling flow direction (i.e., the alloy width direction), forming macroscopically visible segregation bands with significant local concentration variations. This steep compositional gradient induces severe electrochemical inhomogeneity during anodizing. Specifically, the enriched region exhibits enhanced electrochemical activity due to its high Mg content, resulting in a faster oxide film growth rate than the intragranular region, leading to increased film thickness differences. Macroscopically, this manifests as flow lines or banded color difference defects distributed along the alloy width direction. This invention significantly mitigates the concentration gradient by controlling the width of the macroscopic segregation bands above a threshold, reducing the difference in electrochemical activity between the grain boundaries and intragranular regions to an acceptable range, and controlling the dispersion of the anodized film growth rate within a reasonable range, fundamentally eliminating the conditions for color difference formation.

[0070] Furthermore, the concentration difference directly determines the degree of difference in the growth rate of the oxide film in different regions. Therefore, this invention rationally controls the threshold of the concentration difference between adjacent bands based on the growth kinetics of anodic oxide films. When the concentration difference is too high, the difference in oxidation current density between the high-concentration region and the low-concentration region is too large, resulting in a significant increase in film thickness fluctuation. This film thickness difference will produce obvious interference color differences under a specific illumination angle, which macroscopically manifests as a flowing water ripple defect. It is particularly important to note that the band width and concentration difference have a synergistic effect. Even if the band width is sufficient, if the concentration difference is too large, the oxide film may still cause color differences due to abrupt changes in local electrochemical activity. Conversely, even if the concentration difference is small, if the band is too narrow, the enrichment region will be too localized, which may also form obvious electrochemical boundaries. This invention simultaneously controls both within a reasonable range, ensuring a high degree of uniformity in the microscopic composition field.

[0071] Understandably, this invention constructs a specific dual-morphology strengthening phase distribution structure by multi-dimensionally and quantitatively controlling the size, quantity, and relative proportion of the Mg2Si intermetallic compounds precipitated after T6 heat treatment. This helps to achieve synergistic optimization of high strength and excellent anodized appearance in 6-series low-silicon die-cast aluminum alloys.

[0072] It is important to clarify that the "equivalent circle diameter" is a standardized parameter in materials science used to characterize the size of irregularly shaped particles. It is defined as the diameter of a circle with a projected area equal to that of the target particle. This parameter effectively eliminates measurement biases caused by the irregular morphology of precipitated phases and scientifically characterizes their spatial footprint. Based on the projection characteristics of intermetallic compounds on a two-dimensional metallographic observation surface, this invention clearly distinguishes them into two categories and assigns them different functional roles.

[0073] It should be noted that the area ratio mentioned in this invention refers to the percentage of the area occupied by the target phase on the metallographic observation surface to the total observation area, which is an important two-dimensional parameter characterizing its volume fraction.

[0074] Preferably, the aluminum alloy, after undergoing T6 heat treatment, contains two Mg2Si intermetallic compounds, F and G.

[0075] The equivalent circle diameter of intermetallic compound F ranges from 3 μm to 6 μm, and can be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or any value between them. It should be noted that the lower limit of the equivalent circle diameter of intermetallic compound F includes 3 μm; that is, Mg₂Si strengthening phases with an equivalent circle diameter of 3 μm belong to intermetallic compound F.

[0076] Intermetallic compound F, as a coarse reinforcing phase in alloys, primarily functions to provide structural stability, inhibit abnormal grain growth, and contribute to matrix strength. This invention controls the equivalent circle diameter of intermetallic compound F within the range of 3 μm to 6 μm, based on a balance between strengthening effect and anodized surface quality.

[0077] Specifically, when the equivalent circle diameter of intermetallic compound F is less than 3 μm, its size range overlaps with that of intermetallic compound G (0.03 μm~3 μm), leading to blurred boundaries between the two strengthening phases. Coarse phases with excessively small sizes exhibit poor stability during heat treatment, are prone to over-dissolution or uneven coarsening, and struggle to exert their durable role as grain boundary pinning points, resulting in decreased microstructural stability during high-temperature service or subsequent processing. Furthermore, excessively small F phase density often leads to a high overall phase interface area in the matrix, exacerbating micro-electrochemical inhomogeneities during anodizing. When the equivalent circle diameter of intermetallic compound F exceeds 6 μm, the particles are excessively coarse. In terms of mechanical properties, coarse particles easily become stress concentration sources, inducing microcrack initiation during load-bearing and impairing the alloy's plasticity and toughness. Regarding anodizing performance, the significant electrochemical potential difference between coarse particles and the aluminum matrix creates a strong microcouple effect. In sulfuric acid electrolytes, the matrix surrounding coarse phases readily dissolves preferentially, hindering oxide film growth or reducing film thickness in this region. Macroscopically, this manifests as dark spots, pits, or streaks distributed along the grains. Furthermore, the protrusions or depressions formed by excessively large particles on the oxide film surface significantly increase surface roughness, disrupting the uniformity of appearance. Therefore, a size range of 3μm to 6μm ensures that the F phase effectively plays its stabilizing role as a coarse reinforcing phase while keeping its interference with the continuity of the anodic oxide film within acceptable limits.

[0078] The equivalent circle diameter of intermetallic compound G is 0.03 μm to 3 μm; it can be 0.03 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 2.9 μm, or any value between them. It should be noted that the upper limit of the equivalent circle diameter of intermetallic compound G does not include 3 μm.

[0079] Intermetallic compound G, as a fine reinforcing phase in the alloy, primarily contributes to the precipitation strengthening of the matrix and works synergistically with intermetallic compound F to optimize the surface microstructure of the anodic oxide film. This invention controls the equivalent circle diameter of intermetallic compound G within the range of 0.03 μm to 3 μm, based on a balance between the precipitation strengthening mechanism and the density of the anodic oxide film.

[0080] Specifically, when the equivalent circle diameter of intermetallic compound G is less than 0.03 μm, the precipitated phase is too small, and when dislocations move to the precipitated phase, a cut-through mechanism is more likely to occur instead of the Orovan bypass mechanism. The cut-through mechanism consumes less energy, resulting in a significant reduction in precipitation strengthening effect, and the yield strength of the alloy is difficult to meet the requirements of 6-series aluminum alloy structural applications. In addition, precipitated phases that are too small may completely dissolve or overreact during anodizing, failing to form a stable composite structure in the oxide film, leading to uneven optical properties of the film. When the equivalent circle diameter of intermetallic compound G is greater than 3 μm, its size range overlaps with that of intermetallic compound F (3 μm~6 μm), resulting in blurred boundaries between the two strengthening phases. Oversized fine nodules lose their advantage of diffuse distribution and transform into coarse second phases. In terms of anodizing performance, oversized nodules mean a reduction in the number of phase interfaces per unit volume, but the potential difference between a single phase and the matrix expands, easily forming obvious micro-galvanic corrosion centers locally. Furthermore, excessively large particles can create protrusions or depressions on the oxide film surface, significantly increasing surface roughness and compromising appearance consistency. Therefore, a size range of 0.03 μm to 3 μm ensures that the G phase can effectively exert its precipitation strengthening effect as a fine reinforcing phase while controlling its interference with the continuity of the anodic oxide film within the microscale.

[0081] Preferably, the ratio (f / g) of the area fraction f of intermetallic compound F to the area fraction g of intermetallic compound G is 1.5 to 4, and can be 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, or any value between them. This invention introduces the f / g ratio parameter and controls its range to 1.5 to 4.0. This ratio reflects the volume balance between the coarse reinforcing phase (intermetallic compound F) and the fine reinforcing phase (intermetallic compound G), which helps to coordinate mechanical properties and anodizing performance.

[0082] Specifically, intermetallic compound F, as the coarse phase, mainly plays a role in grain boundary pinning, maintaining microstructure stability, and electrochemical buffering during anodic oxidation; intermetallic compound G, as the fine phase, mainly plays a role in matrix precipitation strengthening. The f / g ratio essentially controls the relative contribution weights of these two functional phases in the microstructure.

[0083] When the f / g ratio is below 1.5, it means that the relative content of the coarse phase F is too low, while the relative content of the fine phase G is too high. In this case, although the alloy may achieve a high yield strength, the pinning effect of the coarse phase relative to the grain boundaries is insufficient, leading to a decrease in the microstructural stability of the alloy during high-temperature service or heat treatment, and making the grains prone to abnormal growth. More importantly, during anodizing, the coarse phase F, due to its larger size, has a stronger electrochemical buffering capacity than the fine phase G, and can homogenize the potential difference between the grain boundaries and the intragranular regions. When the F phase content is relatively insufficient, this buffering effect is weakened, the difference in oxidation rate between the grain boundary region and the intragranular region is amplified, and network color difference or flow line defects distributed along the grain boundaries are easily generated. In addition, an excessively high density of fine phases may lead to narrowing of the matrix channels, impairing the plasticity of the alloy.

[0084] When the f / g ratio is higher than 4.0, it means that the relative content of the coarse phase F is too high, while the relative content of the fine phase G is insufficient. In this case, although the grain boundary stability may be good, the volume fraction of micron-scale hard and brittle phases in the microstructure is too large. These coarse phases are prone to becoming the origin of microcracks under load, significantly impairing the plasticity and toughness of the alloy. In terms of anodizing performance, an excessively high coarse phase content means that there are too many heterogeneous interfaces per unit area that are very different from the electrochemical properties of the aluminum matrix. Although a single coarse phase may have a buffering effect, an excessively high interface density will accumulate microcouple effects, leading to an increase in the dispersion of oxide film growth rate. At the same time, the lack of fine reinforcing phase G will lead to a weakening of the matrix precipitation strengthening effect, and the alloy strength will be difficult to meet the structural component application requirements of 6-series aluminum alloys. In addition, an excessively high F phase ratio is often accompanied by an overly dense network structure (if present) or an overly dense distribution of coarse phases, which leads to the matrix being divided into a large number of isolated micro-regions. During anodizing, the film thickness fluctuates due to orientation differences in each micro-region, forming scintillation or streak defects on a macroscopic scale.

[0085] Therefore, controlling the f / g ratio within the range of 1.5 to 4.0 ensures that the continuous network of intermetallic compounds F (preferred morphology) provides the structural framework and electrochemical homogeneity, while the fine, dispersed intermetallic compounds G provide the main precipitation strengthening. The synergistic effect of these two components allows the alloy to achieve high strength while maintaining a surface free of visible color differences, flow lines, or black streaks after anodizing. It should be noted that although the F phase exhibits a continuous network morphology in the preferred embodiment to maximize the above effects, the core of the f / g ratio lies in controlling the volume balance between the coarse and fine phases. This balance is the foundation for achieving synergistic optimization of mechanical properties and anodizing performance.

[0086] Preferably, in any observation area of ​​the aluminum alloy, the sum of the area ratio f of intermetallic compound F and the area ratio g of intermetallic compound G is not less than 1.5%, and can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, higher, and any value between them; more preferably, the sum of the area ratio f of intermetallic compound F and the area ratio g of intermetallic compound G is not less than 2.0%.

[0087] Furthermore, the sum of the area ratios is no greater than 3.0%.

[0088] It should be noted that the sum of area ratios mentioned in this invention specifically refers to the percentage of the total observed area of ​​the sum of the projected areas of intermetallic compounds F and G on the metallographic observation surface. This two-dimensional parameter can effectively characterize the total volume fraction of the Mg2Si strengthening phase precipitated after heat treatment and is a microstructure indicator that relates alloy composition, heat treatment process and final mechanical properties.

[0089] This invention controls the sum of the area ratios to be no less than 1.5% to ensure sufficient precipitation of strengthening phases to improve mechanical properties. For Al-Mg-Si alloys of the 6-series, the yield strength mainly comes from the precipitation strengthening contribution of fine, dispersed Mg2Si precipitates (i.e., intermetallic compound G), while the coarse phase (intermetallic compound F) mainly plays a role in grain boundary pinning and crack deflection. When the sum of the area ratios is less than 1.5%, it means that the total amount of effective strengthening phase per unit volume is insufficient, and the alloy may not be able to achieve the strength level expected for 6-series die-cast aluminum alloys used as structural components. This is usually due to excessively high solution treatment temperature or time, resulting in the complete dissolution of most of the Mg2Si phase, or insufficient aging treatment, resulting in a small number of precipitates. In addition, an excessively low total amount of strengthening phase will also weaken the electrochemical buffering capacity of the alloy during the anodizing process, leading to increased dispersion in the oxide film growth rate, which macroscopically manifests as local color differences or patchy defects with uneven brightness. Therefore, controlling the sum of area ratios to a lower limit of 1.5% helps to give 6-series die-cast aluminum alloys both high strength and excellent anodized appearance.

[0090] Furthermore, based on the principle of mass conservation and precipitation kinetics, the upper limit of the sum of area ratios in this invention is no greater than 3.0%. Specifically, the amount of Mg2Si intermetallic compound formed is limited by the total content of Si and Mg elements in the alloy and their stoichiometric relationship. According to the chemical formula of Mg2Si, by controlling the total content of Si and Mg elements in this invention, the limiting area ratio of Mg2Si intermetallic compounds in the aluminum alloy can be calculated to be approximately 3.2%. Further considering that some Si / Mg will dissolve in the aluminum matrix during actual aging, this invention specifies an upper limit of 3.0% for the sum of area ratios, which should be understood by those skilled in the art.

[0091] Preferably, in any observation region of the aluminum alloy, the area ratio f of the intermetallic compound F satisfies 0.8%≤f≤2.0%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, and any value between them.

[0092] It should be noted that the specific value of f mentioned above needs to be selected in conjunction with the area ratio g of the intermetallic compound G to ensure that the constraints of the f / g ratio being 1.5 to 4 and the sum of the area ratios being 1.5% to 3.0% are met.

[0093] For intermetallic compounds F, if f is below 0.8%, it means that coarse secondary phases are extremely rare. This may stem from near-perfect solution treatment, which, while more beneficial to matrix purity and electrochemical homogeneity, loses the pinning effect of coarse secondary phases on grain boundary migration and the deflection effect on crack propagation paths, potentially adversely affecting the alloy's heat resistance, fracture toughness, and ability to inhibit recrystallization. If f is above 2.0%, it means that there are too many coarse secondary phases with micron-sized components in the microstructure. These phases are not only potential crack initiation sources, but more importantly, during anodizing, they act as heterogeneous phases with different electrochemical properties from the aluminum matrix, inducing severe localized corrosion or selective dissolution. Since micron-sized components are much larger than the initial growth scale of the oxide film, these phases may completely detach in the electrolyte or form deep pits around them, resulting in discontinuous and uneven oxide film thickness at these locations, macroscopically manifesting as unremovable pitting, dark spots, or color differences. Therefore, keeping f within the range of 0.8% to 2.0% aims to preserve its limited positive contribution to microstructure stability and toughness, while suppressing its adverse effects on surface treatment to an acceptable level.

[0094] Preferably, in any observation region of the aluminum alloy, the area ratio g of the intermetallic compound G satisfies 0.3%≤g≤1.2%, and can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, and any value between them.

[0095] It should be noted that the specific value of g mentioned above needs to be selected in conjunction with the area ratio f of the intermetallic compound F to ensure that the constraint of f / g ratio being 1.5 to 4 and the sum of area ratios being 1.5% to 3.0% is met.

[0096] For intermetallic compounds G, this invention controls their area fraction g between 0.3% and 1.2%, which is beneficial for aluminum alloys to achieve high strength (especially high yield strength). For 6-series aluminum alloys, sufficient nano / submicron-scale reinforcing phases are required to achieve sufficiently high tensile strength. When g is below 0.3%, the amount of reinforcing phase is insufficient, and the strength may be difficult to meet the requirements; when g is above 1.2%, although the strength may continue to increase, the precipitated phases are too dense, which may lead to narrowing of the matrix channels, a significant decrease in plasticity, and also increase the number of heterogeneous phases per unit area during anodizing, which is not conducive to overall electrochemical uniformity. Controlling g within the range of 0.3% to 1.2% can simultaneously achieve high strength and good plasticity, and obtain a uniform anodized surface.

[0097] Understandably, the present invention controls the morphological characteristics of intermetallic compounds F and G, which helps to achieve synergistic optimization of the mechanical properties and anodized appearance of 6-series low-silicon die-cast aluminum alloys.

[0098] Preferably, the intermetallic compound F is in the form of a continuous network, and the average mesh size of the continuous network is 5μm to 20μm, which can be 5μm, 7μm, 9μm, 11μm, 13μm, 15μm, 17μm, 19μm, 20μm and any value between them; the average aspect ratio of the network branches in the continuous network is 4.0 to 20.0, which can be 4.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0, 18.0, 20.0 and any value between them.

[0099] The intermetallic compound F exhibits a continuous network morphology, which means that after mechanical polishing and Keller's reagent etching of metallographic samples treated with T6, and then observed by field emission scanning electron microscopy in backscattered electron mode, the Mg2Si phase with an equivalent circle diameter of 3μm~6μm is interconnected along grain boundaries or subgrain boundaries to form a closed or semi-closed network structure surrounding the aluminum matrix grains. This network shows a continuous and interconnected characteristic in two-dimensional projection, with the branch connection length between any adjacent network nodes not less than 3 times the average branch width, and the number of network breakpoints not exceeding 3 in any 100μm×100μm observation area.

[0100] The formation of this continuous network structure originates from the unique solidification and precipitation behavior of 6-series aluminum alloys with a low silicon (0.3%~1.0%) composition. Specifically, during the rapid solidification process of die casting, appropriate amounts of silicon and magnesium preferentially form eutectic Mg2Si phases at the grain boundaries. After solution treatment, some coarse grain boundary phases are not completely dissolved and are retained. During the subsequent aging process, these residual phases act as heterogeneous nucleation sites, promoting the preferential precipitation of Mg2Si along the grain boundaries, ultimately forming a continuous network distribution.

[0101] This continuous network structure can effectively improve the mechanical properties of aluminum alloys. The possible mechanisms of action include: First, the network skeleton effectively pins grain boundaries, significantly inhibiting abnormal grain growth during high-temperature service or heat treatment, and maintaining the fine-grain strengthening effect; Second, the network structure acts as a physical barrier to dislocation movement, forcing dislocations to bypass or pile up when crossing grain boundaries, thereby improving the yield strength and strain hardening capacity of the material; Third, during crack propagation, the continuous network phase can induce cracks to deflect along the network path, increasing the fracture surface energy and improving fracture toughness.

[0102] The average mesh size of the continuous mesh is limited to 5μm~20μm, which refers to the average value of the equivalent circle diameter of the aluminum substrate region surrounded by the mesh structure. This parameter directly reflects the density of the mesh structure.

[0103] When the mesh size is less than 5 μm, the network structure is too dense, dividing the aluminum substrate into numerous isolated micro-regions. During anodizing, the differences in crystal orientation among these micro-regions lead to increased dispersion in the oxide film growth rate, resulting in significant film thickness fluctuations and macroscopically manifesting as scintillation or striped texture defects. Simultaneously, the excessively small mesh size restricts the movement space of dislocations within the substrate, leading to a significant decrease in plasticity. When the mesh size is greater than 20 μm, the continuity of the network structure is disrupted, exhibiting a discontinuous distribution. This significantly weakens the pinning effect on grain boundaries, making the grains prone to abnormal growth during subsequent heat treatment or service, resulting in decreased strength. Furthermore, the sparse network structure amplifies the difference in electrochemical activity between the grain boundary regions and the intragranular regions, easily forming a network-like color difference distributed along the grain boundaries during anodizing. A mesh size range of 5 μm to 20 μm ensures that the network structure possesses sufficient continuity to exert its grain boundary strengthening and stabilizing effects while avoiding electrochemical inhomogeneities caused by excessive substrate segmentation.

[0104] The average aspect ratio of the continuous network branches is limited to 4.0–20.0, referring to the average ratio of the longest axis of a single branch constituting the continuous network structure to the largest dimension perpendicular to that axis. This aspect ratio range reflects the morphological characteristics of the branches being slender strips or needle-like plates, which is closely related to the preferential growth habit of the Mg2Si phase along specific crystallographic directions of the aluminum matrix. The slender branch morphology, on the one hand, allows for the formation of an effective continuous network at a relatively low area ratio due to its high aspect ratio, avoiding excessive matrix segmentation caused by excessive area ratio; on the other hand, the slender branches exhibit relatively uniform anisotropic dissolution during anodizing, preventing the formation of significant current concentration points at the tips or corners, thus avoiding abnormal local oxide film growth.

[0105] When the aspect ratio is below 4.0, the branches tend to be equiaxed, requiring a higher area ratio to form a continuous network. This increases the degree of segmentation of the coarse relative to the matrix, impairing plasticity and exacerbating anodizing inhomogeneity. When the aspect ratio exceeds 20.0, the branches become too thin and fragile, easily breaking under the stress of oxide film growth, forming microcrack sources, and reducing film adhesion and durability. Within the aspect ratio range of 4.0 to 20.0, the network structure maintains mechanical stability while minimizing interference with the anodizing process.

[0106] Preferably, the intermetallic compound G is in the form of needles with an aspect ratio of 5 to 10, which can be 5, 6, 7, 8, 9, 10 and any value between them.

[0107] It should be noted that the aspect ratio can be determined by observing the T6 state sample in backscattered electron mode using a field emission scanning electron microscope. At least 10 fields of view should be randomly selected, and the major and minor axis dimensions of at least 50 precipitates of the same type should be counted in each field of view and the average ratio should be calculated to ensure the statistical representativeness and repeatability of the results.

[0108] This invention controls the intermetallic compound G to have a needle-like morphology with an aspect ratio of 5-10. This refers to the dispersed distribution of fine Mg₂Si phases with an equivalent circle diameter of 0.03 μm-3 μm within the aluminum matrix, exhibiting elongated needle-like or rod-like shapes, with the ratio of their major axis to minor axis concentrated in the range of 5-10. This morphological characteristic corresponds to the β'' transition phase or fine β-Mg₂Si phase formed after optimized aging of 6-series aluminum alloys, and is a major contributor to precipitation strengthening. Due to its high aspect ratio, the needle-like precipitate can interact strongly with moving dislocations. Specifically, dislocations cannot directly cut through the needle-like phase and are forced to bypass it, leaving dislocation loops around the phase. This Orovan bypass mechanism can significantly improve the yield strength of the material.

[0109] By controlling the aspect ratio of the needle-like morphology to be 5-10, sufficient strengthening efficiency of the precipitated phase is ensured, while avoiding the weakening effect caused by too low an aspect ratio or the damage to plasticity caused by excessive anisotropy enhancement due to too high an aspect ratio. During the anodizing process, the needle-like phases within the size range and aspect ratio range of the intermetallic compound G, due to their small absolute size, scatter incident light uniformly and diffusely, without producing macroscopic optical inhomogeneities. At the same time, during the oxide film growth process, these small needle-like phases can be partially encapsulated or assimilated by the newly formed alumina, forming a uniformly embedded Al-Mg-Si-O composite structure. This not only does not disrupt the continuity of the film layer, but also optimizes the surface optical properties by controlling the light scattering behavior, giving the oxide film a soft and uniform metallic texture.

[0110] Preferably, the dispersion density of the Mg2Si intermetallic compound is 10 particles / μm. 2 ~200 cells / μm 2 It can be 10 / μm 2 30 cells / μm 2 50 cells / μm 2 80 cells / μm 2 100 cells / μm 2 150 cells / μm 2 200 / μm 2 And any values ​​in between.

[0111] Understandably, the present invention controls the dispersion density of the Mg2Si intermetallic compound to be 10 particles / μm. 2 ~200 cells / μm 2 Together with the aforementioned dual-morphological size distribution, area ratio, and f / g ratio, this constitutes a further microstructure characterization system.

[0112] It should be noted that the dispersion density refers to the area per unit observation (μm²) observed on the aluminum alloy metallographic sample after T6 heat treatment using a field emission scanning electron microscope in backscattered electron mode, and automatically identified and counted using image analysis software. 2The number of independent particles of all Mg2Si intermetallic compounds (including intermetallic compounds F and G) within the sample must be counted. At least five fields of view must be selected at different locations on the sample, with each field of view having an area ≥100 μm. 2 The average value is taken as the final result.

[0113] It should be noted that for intermetallic compounds F exhibiting a continuous network morphology, this invention employs a network node counting method for statistical analysis: the continuous branch segments between adjacent three- or four-pronged intersections in the network structure are regarded as an independent statistical unit. This method avoids misjudging the entire continuous network as a single particle, which would lead to a severe underestimation of density, and also prevents the excessive division of the network branches into multiple particles, which would lead to an artificially high density. This ensures the applicability and repeatability of the dispersion density parameter in the network-dominated strengthening phase system of 6-series aluminum alloys.

[0114] Preferably, the dispersion density is controlled at 10 particles / μm. 2 ~200 cells / μm 2 Within this range, it helps to achieve synergistic optimization of mechanical properties and anodized appearance in 6-series low-silicon composition systems.

[0115] When the dispersion density is less than 10 particles / μm 2 This indicates a severe deficiency or excessive coarsening of the overall amount of reinforcing phase in the microstructure. This is usually due to excessively high solution treatment temperature or time, leading to the complete dissolution of most of the Mg2Si phase, or insufficient aging treatment resulting in a sparse number of precipitated phases. Under these circumstances, the tensile strength of the alloy is difficult to meet the requirements, and the yield strength is significantly reduced, failing to meet the mechanical requirements of consumer electronics structural components. At the same time, excessively low dispersion density means that there are a large number of regions in the matrix without reinforcing phase distribution. During the anodizing process, these regions lack the electrochemical buffering effect of fine precipitated phases, resulting in a significant difference in oxide film growth behavior compared to the phase-containing regions. This leads to increased film thickness fluctuations, which macroscopically manifest as patchy defects with local color differences or uneven brightness.

[0116] When the dispersion density is higher than 200 particles / μm 2When the density of precipitates is too high and their size is generally small, it indicates that the precipitates are excessively numerous and generally small in size, which usually corresponds to the early stage of over-aging or insufficient solid solution. Although high-density fine phases can provide excellent strength, excessively high phase interface density will significantly increase the micro-electrochemical inhomogeneity in the matrix: during the anodizing process, there is a small potential difference at the interface between each Mg2Si phase and the aluminum matrix. When there are too many such interfaces per unit area, the local current density fluctuations are accumulated and amplified, resulting in increased dispersion of the oxide film growth rate. At the same time, high-density precipitates divide the aluminum matrix into a large number of small regions. The differences in oxidation rate between these regions due to differences in crystal orientation cannot be effectively homogenized by the phase interfaces, ultimately resulting in a visible shimmering or hazy appearance under certain lighting angles. In addition, excessively high dispersion density is often accompanied by generally small precipitate size. These ultrafine phases are easily completely dissolved during the anodizing process and cannot form an Al-Mg-Si-O composite structure that is beneficial to the optical properties of the oxide film, resulting in a decrease in film gloss.

[0117] This invention controls a suitable dispersion density range through a low-silicon (0.3%~1.0%) composition design, T6 heat treatment, and a dual-morphology strengthening phase structure. Under low-silicon conditions, the amount of the original Mg2Si phase formed during alloy solidification is relatively limited. After T6 heat treatment, a synergistic distribution of a continuous network of intermetallic compounds F with a suitable area ratio and fine needle-like intermetallic compounds G can be formed. In this microstructure, the two precipitated phases together ensure that the total dispersion density stably falls within a suitable dispersion density range. This density range ensures that the strengthening phase is neither too sparse in space, leading to insufficient mechanical properties and electrochemical uniformity, nor too dense, causing disordered anodic oxide film growth.

[0118] After anodizing, the aluminum alloy has an anodized film on its surface, and the arithmetic mean height Sa of the anodized film is 0.1μm~0.5μm, which can be 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm and any value between them; The average width Rsm of the contour unit is 0.5μm to 10μm, and can be 0.5μm, 1μm, 2μm, 4μm, 6μm, 8μm, 10μm and any value between them.

[0119] Understandably, the present invention controls the arithmetic mean height Sa of the anodic oxide film to be 0.1 μm to 0.5 μm and the average width Rsm of the contour unit to be 0.5 μm to 10 μm. These are quantitative parameters characterizing the surface microstructure quality of 6-series low-silicon die-cast aluminum alloys after anodizing. This combination of parameters determines the appearance quality of the product in high-end consumer electronics applications.

[0120] It should be noted that the arithmetic mean height Sa mentioned in this invention is a three-dimensional surface roughness amplitude parameter defined according to the ISO 25178 standard. Its physical meaning is the arithmetic mean of the absolute values ​​of the heights of all data points relative to the least squares reference surface within the evaluation area. The average width Rsm of the profile unit mentioned in this invention is a two-dimensional profile spacing parameter defined according to the ISO 4287 standard, used to evaluate the arithmetic mean of the width of the profile unit (i.e., the horizontal projection distance between adjacent profile peaks and valleys) within a length. In specific testing, a white light interferometer or confocal microscope can be used to acquire the three-dimensional surface morphology data. The evaluation area should have no less than 5 fields of view (each field of view area ≥ 100μm × 100μm). Measurements should be taken along the direction perpendicular to the die-casting filling to avoid interference from flow marks. The final result is the average value of all fields of view.

[0121] This invention controls the Sa value within the range of 0.1μm to 0.5μm, which helps 6-series aluminum alloys achieve a balance between ideal optical performance and process economy under low silicon content conditions. When Sa < 0.1μm, the surface is too smooth, approaching a mirror state, which places excessive demands on the original surface quality of the die-casting substrate (requiring additional mechanical or chemical polishing, significantly increasing manufacturing costs). At the same time, excessively low micro-undulations cannot effectively scatter incident light, resulting in an excessively high proportion of specular reflection, producing glare at certain lighting angles, and destroying the soft, understated metallic texture sought after by high-end electronic products. In addition, excessively low Sa values ​​may also result in the lack of necessary micro-anchoring structures on the surface, reducing the adsorption stability of dye molecules during subsequent coloring processes, leading to insufficient color saturation and decreased color fastness.

[0122] When Sa > 0.5 μm, the surface micro-peaks and valleys are too large, resulting in irregular and high-intensity diffuse reflection of incident light, which appears hazy or powdery on a macroscopic level, and the gloss is significantly reduced. Moreover, excessively high Sa values ​​often originate from the amplification of the matrix microstructure inhomogeneity (such as excessive grain size standard deviation, numerous porosity defects, or disordered distribution of the Mg2Si strengthening phase) during the anodizing process. These micro-defects cause significant fluctuations in the oxide film growth rate in local areas, forming visible watermarks or striped texture defects. The Sa range of 0.1 μm to 0.5 μm ensures that the surface has moderate micro-undulations, which can eliminate glare through uniform diffuse reflection and present a soft metallic luster, while maintaining the compactness and optical uniformity of the film structure.

[0123] This invention controls Rsm within the range of 0.5μm to 10μm, which helps to control the spatial distribution characteristics of the surface micro-texture. When Rsm < 0.5μm, it indicates that the surface contour undulations are too dense and fragmented, usually due to the excessively sharp segregation of magnesium at the grain boundaries in the matrix. This amplifies the difference in oxidation rates between the grain boundaries and the intragranular regions during anodizing, forming high-frequency micro-undulations, which macroscopically manifest as a blackened surface or a lack of texture depth. When Rsm > 10μm, it indicates that there are large-scale periodic undulations on the surface, usually related to uneven advancement of the molten front during die casting, forming macroscopic flow marks, or due to the projection amplification effect of large pores on the oxide film surface. Such large-spacing undulations will produce alternating light and dark striped visual defects under specific lighting angles.

[0124] This invention utilizes the synergistic effect of an Rsm range of 0.5μm to 10μm and a Sa range of 0.1μm to 0.5μm to create a uniform and fine micro-texture structure on the oxide film surface. This avoids glare caused by specular reflection and eliminates stripe defects caused by large-scale undulations, ultimately resulting in a visually pure and high-end textured surface that meets the stringent requirements of products such as smartphone frames and tablet back panels.

[0125] Preferably, the a* value of the surface color of the anodized die-cast aluminum alloy is less than 0.1, and can be 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, smaller, or any value between them; b* < 1.0, and can be 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, smaller, or any value in between; L* < 25, and can be 24, 22, 20, 18, 16, 14, 12, 10, smaller, or any value in between.

[0126] Understandably, the present invention limits the surface color of anodized die-cast aluminum alloy to a* < 0.1, b* < 1.0, and L* < 25. This is a quantitative characterization of the surface color of 6-series low-silicon die-cast aluminum alloy after anodizing based on the CIELAB color space. This parameter combination directly reflects the comprehensive level of the uniformity of the matrix microstructure and the stability of the anodizing process, and is an important indicator for evaluating the appearance quality of high-end consumer electronics products. The CIELAB color space (based on ISO 11664-4 standard) is a color characterization system based on the uniformity of human visual perception. L* represents lightness, with a value range of 0~100. L*=0 corresponds to an ideal black body, and L*=100 corresponds to an ideal white body. a* represents the red-green axis coordinate, with positive values ​​leaning towards red and negative values ​​leaning towards green. a*=0 is neutral gray. b* represents the yellow-blue axis coordinate, with positive values ​​leaning towards yellow and negative values ​​leaning towards blue. b*=0 is neutral gray. The a*, b*, and L* parameters described in this invention are measured using a standard spectrophotometer. Under the conditions of a D65 standard light source (simulated sunlight) and a 10° standard observer, measurements are taken at different locations on the product surface (at least 5 points, including the central area, the edge area, and areas with different filling directions). The arithmetic mean is taken as the final result to eliminate the influence of local measurement fluctuations on the evaluation results.

[0127] For many high-end consumer electronics products (such as dark-colored casings like space gray, dark blue, and black), the anodized surface aims for a deep texture with low brightness and low saturation. This invention limits L* to < 25, ensuring a dark surface tone that aligns with the aesthetic trends of high-end products. Limiting a* to < 0.1 and b* to < 1.0 means the surface color is very close to neutral colors, almost devoid of red, green, or yellow hues. This indicates that the anodized film of this invention is inherently very pure, without color shift caused by selective absorption or reflection of specific wavelengths of light due to matrix component segregation, impurity phases, or process fluctuations.

[0128] Preferably, the incidence of surface defects in the anodic oxide film is below 0.05%, and can be 0.05%, 0.04%, 0.03%, 0.02%, 0.01%, and lower, or any value between them.

[0129] This invention also provides an appearance inspection standard that is closer to actual quality control. The anodized surface is visually inspected, and the percentage of any visible defects (including but not limited to color difference, bright spots, dark spots, textures, and contamination) relative to the total surface area is counted, requiring it to be below 0.05%. This is a visual yield requirement, which more comprehensively reflects the product's appearance than a simple color difference value. The high-quality anodized film of this invention meets the appearance quality standards of the consumer electronics industry.

[0130] Preferably, the solidification point of the anodized die-cast aluminum alloy is in the range of 570℃~620℃, and can be 570℃, 580℃, 590℃, 600℃, 610℃, 620℃ and any value between them.

[0131] The aforementioned solidification point range can be understood as the liquidus temperature range of the alloy, or the temperature at which substantial solidification begins, as measured by thermal analysis. For 6-series aluminum alloys, the solidification point is mainly affected by the Si and Mg content. Controlling the solidification point range to 570℃~620℃ is a thermophysical result that matches the aforementioned composition design of 0.3%~1.0% Si and 0.4%~1.5% Mg. A suitable solidification point means that the melt has a suitable superheat at the injection temperature. If the solidification point is too low, the superheat is too great at the same pouring temperature, resulting in excessive heat in the melt, which may lead to slow solidification, coarse grains, and significant thermal shock to the mold. If the solidification point is too high, a higher pouring temperature is required to ensure fluidity, which increases energy consumption, exacerbates element burn-off and gas absorption tendency, and may also cause chilling defects due to excessive temperature difference with the mold. The solidification point range of 570℃ to 620℃ allows the alloy to achieve stable filling and sequential solidification with reasonable superheat when using subsequent optimized die casting processes. This is beneficial for obtaining uniform, fine-grained, and dense die castings with good formability and microstructure quality.

[0132] It should be clarified that the core of the protection of the anodized die-cast aluminum alloy in this invention lies in its unique microstructural characteristics, rather than being entirely limited to a specific manufacturing process. Regardless of the manufacturing method used, any metal alloy possessing the specific microstructural characteristics described in this invention should be considered to fall within the scope of protection of this invention. Manufacturing methods include, but are not limited to: employing different melt filling strategies with varying timing or paths; using local pressurization methods based on different principles such as mechanical, hydraulic, or pneumatic pressure; controlling the solidification sequence through special mold cooling design combined with pressure intervention; and performing appropriate local solid-state thermomechanical treatment (such as warm forging or rolling) after conventional die casting to further eliminate edge defects, or combinations thereof. However, despite the existence of multiple possible implementation paths, this invention provides a preferred manufacturing method. After extensive experimental verification, an optimal process window has been determined, enabling the stable and efficient achievement of the aforementioned stringent microstructural control indicators. Below, to better realize and explain in detail how to efficiently and reliably prepare the metal alloy of this invention, an optimized and verified die-casting method embodiment is provided, along with its technical details and principles. This embodiment not only demonstrates the specific operational steps for realizing the product of the present invention, but also reveals the intrinsic relationship between process parameters and microstructure evolution, providing reproducible technical guidance for those skilled in the art.

[0133] In a second aspect, the present invention provides a method for preparing the anodized die-cast aluminum alloy of the first aspect, comprising the following steps: Step S102: After melting the metal alloy to form a molten liquid, the molten liquid includes the following elements by mass percentage: 0.3%~1.0% Si, 0.4%~1.5% Mg, the total content of unavoidable impurities is not greater than 0.3%, and the balance is Al; The molten liquid is kept at a first temperature, and the mold is kept at a second temperature lower than the first temperature. The temperature difference between the first and second temperatures is in the range of 300℃~350℃, and can be 300℃, 305℃, 310℃, 315℃, 320℃, 325℃, 330℃, 335℃, 340℃, 345℃, 350℃, and any value between them.

[0134] Step S102 includes alloy smelting, composition control, and crucial temperature difference control. First, the raw materials are batched and smelted according to the aforementioned low silicon and specific magnesium ratio to ensure that the final melt composition meets the requirements and the total impurities are controlled to ≤0.3% to ensure the purity of the matrix.

[0135] After melting, the molten metal needs to be held at a first temperature. The first temperature is the holding temperature of the molten metal, preferably ranging from 650°C to 720°C, including 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, and any value between them. This temperature range is chosen to ensure the molten metal has sufficient superheat and good fluidity to cope with the potential decrease in fluidity caused by low silicon content, while avoiding excessively high temperatures that could lead to accelerated magnesium loss or severe gas absorption by the melt. The mold needs to be held at a second temperature lower than the first temperature. The second temperature is the mold temperature, preferably ranging from 300°C to 420°C, including 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, and any value between them.

[0136] This invention controls the temperature difference between the melt temperature (first temperature) and the mold temperature (second temperature) within the range of 300℃ to 350℃ based on solidification rate, surface defect formation, and internal microstructure uniformity. This creates optimized thermodynamic conditions for the solidification process of the melt, ensuring that the casting achieves a uniform microstructure and good surface quality. Specifically, the temperature difference is the main driving force for melt solidification. If the temperature difference is too small, the driving force is insufficient, resulting in slow overall cooling of the melt and prolonged solidification time. This not only reduces production efficiency but also provides time for grain growth, leading to the formation of coarse grain structures, which is detrimental to the improvement of mechanical properties. At the same time, an excessively low temperature difference may cause the solidified shell formed at the melt front to be too thin or lack strength, and it may still shift under the subsequent push of the melt. Conversely, if the temperature difference is too large, the melt will undergo severe supercooling upon contact with the mold, rapidly forming a thick and brittle primary solidified shell on the surface of the casting. This shell is extremely prone to cracking under the thermal stress and mechanical action of the subsequent molten metal. Its fragments are trapped in the molten metal or accumulate on the surface, resulting in surface defects such as black streaks. In addition, excessive temperature difference will generate strong temperature gradient and thermal stress inside the casting, which may not only cause deformation or thermal cracking, but also aggravate the segregation of solute elements and promote the directional growth of columnar crystals, which is not conducive to the formation of uniform and fine equiaxed crystals.

[0137] Controlling the temperature difference within the range of 300℃ to 350℃ effectively avoids the aforementioned problems. This temperature difference provides a suitable cooling intensity, ensuring the necessary solidification rate to obtain refined grains while avoiding surface defects and internal stress concentration caused by excessive cooling. Under these conditions, the molten metal forms an initial solidified layer of suitable thickness and strength upon contact with the mold. This relatively stable layer helps resist the slight erosion from subsequent molten metal, protecting surface quality. Simultaneously, the molten metal inside the casting has ample time for relatively uniform heat dissipation and solidification in this relatively mild cooling environment, which is conducive to the nucleation and uniform growth of equiaxed crystals.

[0138] Step S104: Inject the molten liquid into the mold cavity. After the mold cavity is filled, maintain pressure and open the mold to obtain the die-cast aluminum alloy. The velocity of the molten metal injected into the mold cavity shall not exceed 2 m / s, and can be 2 m / s, 1.9 m / s, 1.8 m / s, 1.7 m / s, 1.6 m / s, 1.5 m / s, 1.4 m / s, 1.3 m / s, 1.2 m / s, 1.1 m / s, 1.0 m / s, 0.9 m / s, 0.8 m / s, 0.7 m / s, 0.6 m / s, 0.5 m / s, 0.4 m / s, 0.3 m / s, etc. The moving speed of the molten liquid surface within the mold cavity relative to the mold cavity is no greater than 0.5 m / s, and can be 0.5 m / s, 0.45 m / s, 0.4 m / s, 0.35 m / s, 0.3 m / s, 0.25 m / s, 0.2 m / s, 0.15 m / s, 0.1 m / s, 0.05 m / s, and any value between them.

[0139] Preferably, the velocity of the molten metal injected into the mold cavity is no greater than 1.0 m / s, and the moving velocity of the molten metal surface relative to the mold cavity is no greater than 0.4 m / s. More preferably, the velocity of the molten metal injected into the mold cavity is no greater than 0.5 m / s, and the moving velocity of the molten metal surface relative to the mold cavity is no greater than 0.3 m / s. Even more preferably, the velocity of the molten metal injected into the mold cavity is no greater than 0.3 m / s, and the moving velocity of the molten metal surface relative to the mold cavity is no greater than 0.2 m / s.

[0140] In this invention, the "velocity of molten metal injected into the mold cavity" specifically refers to the flow velocity of the molten metal at the inlet cross-section at the instant it enters the mold cavity through the inlet during filling. This invention controls the filling flow rate and the rising velocity of the molten metal surface within the mold cavity, effectively achieving laminar flow filling and eliminating turbulence and air entrapment. Traditional die-casting processes, in pursuit of filling efficiency, often employ high-speed jets (typically much higher than 2 m / s), causing the molten metal to generate strong inertial and shear forces upon entering the cavity, rapidly transforming the flow state into disordered turbulence. This turbulence not only tears apart the molten metal front, breaking up air within the cavity and entraining it into the melt to form bubbles that are difficult to expel, but also violently erodes the surface of the thin solidified layer that has already formed in contact with the low-temperature mold wall, causing this solidified layer to shift and accumulate, resulting in macroscopic black streaks and watermarks on the product surface. This invention sets the upper limit of the molten metal injection velocity into the mold cavity to no more than 2 m / s precisely to suppress the generation of this destructive flow from the inlet. When the molten metal enters the mold cavity smoothly at a speed not exceeding 2 m / s, its Reynolds number decreases significantly, allowing the flow pattern to transition from turbulent to laminar or steady flow. This velocity threshold makes subsequent smooth filling possible. Building upon this, the proposed optimal range reflects a deeper understanding of the low-speed concept. The lower the velocity, the weaker the inertial force of the molten metal, the gentler the flow, and the less disturbance it causes to the gas inside the mold cavity and the mold surface. For example, in fields with extremely high surface finish requirements, such as consumer electronics casings, using an extremely low filling speed of ≤0.3 m / s can almost completely eliminate surface defects caused by flow impact.

[0141] Furthermore, the movement speed of the molten liquid surface relative to the mold cavity is a key parameter that complements the speed of molten liquid injection into the mold cavity. Understandably, this "movement speed" specifically refers to the rate of advancement of the molten liquid front within the mold cavity space, that is, the instantaneous speed at which the liquid level height or flow extension length corresponding to the volume of molten liquid filling the cavity changes per unit time. The movement speed of the molten liquid surface relative to the mold cavity describes how quickly the solid-liquid interface (i.e., the molten liquid front) advances within the cavity space during the filling process. Understandably, an excessively fast ascent speed means that the molten liquid front covers an excessively large area of ​​the mold per unit time, and the heat exchange process between the molten liquid and the cryogenic mold is too rapid. This leads to two main problems: first, a sudden drop in local temperature at the molten liquid front forms an unstable and unevenly thick initial solidified shell, which is easily broken by subsequent molten liquid, resulting in defects; second, air is rapidly compressed and expelled, unable to be completely discharged through the overflow port, increasing the risk of being trapped. Limiting the liquid surface rise velocity to below 0.5 m / s ensures that the solidification front advances at a uniform and controllable speed, allowing sufficient time for gas to be discharged to the overflow port and making the heat transfer process more uniform. This promotes sequential solidification and fundamentally avoids watermarks and black streaks caused by friction of the solidified layer. Similarly, its preferred range is for those seeking higher surface quality and internal purity.

[0142] Understandably, simultaneously controlling both the speed of molten metal injection into the mold cavity and the speed of molten metal surface movement is essential for ensuring high-quality filling. The speed of molten metal injection into the mold cavity reflects the initial flow state of the molten metal as it enters the cavity from the inlet, while the speed of molten metal surface movement describes the overall behavior of the solid-liquid interface advancing within the cavity. These two parameters are physically different and are influenced by different factors; therefore, they must be controlled collaboratively to achieve the desired filling effect. Controlling only the speed of molten metal surface movement without controlling the speed of molten metal injection into the mold cavity will not effectively solve the problem. If the flow velocity at the inlet is too high, the molten metal will form a divergent and disordered flow front in the initial stage of entering the cavity, disrupting the stability of the entire filling process. Even if the overall surface rise speed is slow, the high-speed injection of molten metal will create severe turbulence in the area near the inlet, directly eroding the thin solidified layer formed on the mold surface, producing black streaks and surface defects. At the same time, the turbulence at the inlet will disrupt the flow order of the molten metal, rendering subsequent control of the surface movement speed meaningless.

[0143] The cross-sectional area of ​​the flow channel varies within ±10% between the position where the liquid inlet contacts the mold cavity and the position where it is far from the mold cavity. It can be ±10%, ±9%, ±8%, ±7%, ±6%, ±5%, ±4%, ±3%, ±2%, ±1%, 0, and any value between them.

[0144] This invention requires that the cross-sectional area variation of the flow channel between the position where the liquid inlet contacts the mold cavity and the position where it is far from the mold cavity be controlled within ±10%. This structural limitation is the physical prerequisite for the subsequent low-speed and stable filling achieved by this method. This feature defines the geometry of the entire molten metal delivery path from the output end of the injection mechanism to the mold cavity inlet.

[0145] This invention requires that the cross-sectional area variation of the flow channel between the position where the liquid inlet contacts the mold cavity and the position where it is far from the mold cavity be controlled within ±10%. Controlling the above parameters is the physical prerequisite for this method to achieve a "gateless" structure and ensure that subsequent low-speed and stable filling can be achieved. This feature defines the geometry of the entire molten metal delivery path from the output end of the injection mechanism to the mold cavity inlet.

[0146] Understandably, "the position in contact with the mold cavity" refers to the interface where the end of the runner directly connects to the mold cavity, i.e., the inlet section where the molten metal finally enters the cavity. "The position away from the mold cavity" refers to any reference section upstream of the runner, typically the starting point where the injection cylinder or pressure chamber connects to the runner, or any section of the runner with a relatively stable cross-sectional area. The "interval runner" refers to a continuous channel segment connecting the two positions along the direction of molten metal flow, not just the section at the endpoints. "Cross-sectional area variation within ±10%" means that, over the entire length of the runner between these two positions, the maximum positive or negative deviation of the area of ​​any cross-section compared to a reference cross-sectional area (usually the inlet section or the starting section) does not exceed 10% of that reference cross-sectional area. Understandably, the inlet section here is usually the section where the inlet runner and the injection chamber in the injection mechanism directly connect. This means that the flow channel is designed as a pipe with a constant or nearly constant cross-section, or a channel where the cross-sectional area changes only very gently and gradually, without any artificially created necks or gates with drastically reduced cross-sectional area. Based on this, the constraint ensures that there are no local throttling points inside the flow channel, thereby eliminating the structural basis for passively amplifying the flow velocity due to abrupt changes in cross-section.

[0147] Understandably, if the cross-sectional area of ​​the runner changes beyond this range, for example, if a local shrinkage of more than 10% occurs, even if the shrinkage ratio is less than that of a conventional gate, a significant Venturi effect will still occur at that location, leading to an increase in local flow velocity. This local acceleration will disrupt the smooth flow state of the molten liquid, potentially initiating turbulence prematurely within the runner or upon entering the cavity. This undermines the laminar or stable flow filling intent pursued by this invention, rendering all subsequent process controls based on the low-speed assumption (such as liquid surface movement speed control and dynamic overflow control) meaningless. Therefore, the strict ±10% limit eliminates the geometric conditions that could cause uncontrollable acceleration from the structural source of fluid transport, and is crucial to ensuring that the molten liquid can smoothly enter the cavity at its original or near-original velocity.

[0148] Understandably, this smooth runner design eliminates the "gate" as a separate structural component with a specific shrinkage function within the mold, thus physically achieving a "gateless" system. It changes the fundamental mode of molten metal injection, shifting from traditional high-pressure, high-speed jetting to a smooth, stable introduction. This is not merely a structural simplification, but a fundamental change in flow control philosophy. It ensures that the kinetic energy of the molten metal entering the cavity is known and controllable, creating the prerequisite for smooth, laminar flow filling throughout the entire cavity.

[0149] The ratio between the overflow of the melt filling and the volume of the mold cavity shall not be less than 0.1, and may be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, higher, and any value between them.

[0150] Preferably, the ratio between the overflow rate of the molten filling and the volume of the mold cavity is in the range of 0.1 to 0.5, and can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, and any value between them. More preferably, the ratio between the overflow rate of the molten filling and the volume of the mold cavity is in the range of 0.1 to 0.2.

[0151] Understandably, this invention, based on the flow dynamics and solidification behavior of 6-series low-silicon aluminum alloy melt within the mold cavity, determines the critical proportional relationship between overflow and mold cavity volume. This proportional limitation helps improve the internal density of die-cast parts and reduce anodized surface defects.

[0152] Specifically, the overflow flow rate serves to directionally expel the cold melt residue, oxide inclusions, and entrained gas formed at the filling front due to contact with the low-temperature mold wall during the final stage of filling. For the low-silicon (0.3%~1.0%) 6-series aluminum alloy described in this invention, although the reduction in silicon content significantly improves anodizing performance, it also leads to a decrease in melt fluidity compared to traditional high-silicon die-casting alloys. The melt front is more prone to forming a high-viscosity oxide scale or cold shut layer due to temperature drop. If these cold shut layers remain inside the casting body or near the surface, the difference in electrochemical behavior between the oxide scale and the substrate will be significantly amplified during subsequent anodizing, manifesting as visible black streaks, flow lines, or color difference defects.

[0153] Understandably, in order to minimize the removal of the cold contaminant layer at the leading edge of the mold cavity, this invention controls the lower limit of the overflow flow rate to the mold cavity volume to be no less than 0.1. During the die casting filling process, no matter how smoothly the liquid surface velocity is controlled (e.g., ≤0.5m / s as specified in this invention), heat exchange will inevitably occur at the moment the molten front edge contacts the mold, forming a solidified or semi-solidified layer with a lower temperature, poorer fluidity, and rich in oxides. If the overflow flow rate ratio is too low, it means that the volume of molten liquid used for flushing and replacement is insufficient, and this portion of the cold contaminant molten liquid at the leading edge cannot be completely pushed into the overflow channel. If the residual cold contaminant molten liquid remains inside the casting body or in the near-surface area, it will cause defects such as cold shuts, flow marks, and porosity in the casting, and significantly reduce the mechanical properties and density of the casting. Especially in the gateless, gentle runner design adopted in this invention (runner cross-sectional area variation within ±10%), although turbulent air entrapment is reduced from the source, sufficient overflow flow rate is still required to ensure the purity of the filling leading edge. Therefore, unlike existing technologies, this invention significantly increases the overflow flow rate, thereby promoting thorough cleaning of the mold cavity, obtaining high-quality castings, and providing a defect-free matrix for subsequent anodizing.

[0154] Building upon this, the present invention further provides a preferred overflow ratio range of 0.1 to 0.5. This range is designed to ensure an optimal balance between process effectiveness, mold design rationality, and production costs. When the overflow ratio is too low, as mentioned earlier, the amount of molten metal available for venting gas and cold slag is insufficient, making it difficult to consistently ensure adequate purification of the cavity under all process conditions. This increases the risk of porosity or inclusions in the casting, leading to a decrease in yield. Conversely, when the overflow ratio is too high, although a larger overflow may technically contribute to the purification effect, it leads to a significant decrease in metal utilization and an increase in raw material costs. Furthermore, an excessively large overflow requires the design of a larger overflow channel (cavity), which not only places higher demands on the spatial layout and structural strength of the mold design, increasing the difficulty and cost of mold manufacturing, but may also increase the processing burden of subsequently removing overflow waste, reducing production efficiency. Therefore, the range of 0.1 to 0.5 defines a reasonable operating range that is technically effective in ensuring quality and economically feasible in production.

[0155] Based on this, the present invention further specifies a preferred ratio range of 0.1 to 0.2. Under the condition of satisfying other core process parameters of the present invention (such as a molten metal temperature difference of 300℃ to 350℃ between the molten metal and the mold, and an injection speed ≤ 2m / s), controlling the overflow ratio within the range of 0.1 to 0.2 can more stably obtain high-quality castings with low porosity and uniform microstructure. This is because under the low-speed, stable filling strategy of the present invention, most of the gas in the cavity has been orderly discharged; the main task of the overflow stage is to fill the remaining space and perform overflow flushing. An overflow rate of 0.1 to 0.2 is sufficient to discharge the small amount of cold-staining molten metal generated in the final stage, while avoiding energy consumption and material waste caused by excessive overflow. This preferred range reflects the optimized choice between high quality and high efficiency in the process of the present invention, which helps to achieve large-scale stable production.

[0156] It is important to note that maintaining a ratio of at least 0.1 between the overflow rate of the molten metal and the volume of the mold cavity is a mandatory requirement for achieving the desired technical effect in the preferred preparation method of this invention, constituting the fundamental safety boundary of the process scheme. The formula provided below regarding the specific functional relationship between the overflow rate and the mold cavity volume represents a preferred dynamic control strategy. In other words, those skilled in the art, when implementing the preferred preparation method of this invention, must first ensure that the overflow rate ratio meets the mandatory requirement of at least 0.1. Based on this, to obtain better process matching and casting quality consistency, a more precise overflow rate ratio can be determined using this formula according to specific process conditions (such as temperature difference and flow rate). If the ratio calculated by the formula is lower than 0.1, the lower limit of 0.1 should be followed to ensure that the process remains within a safe process window. This control logic, which uses absolute values ​​as a baseline and empirical formulas as optimization guidance, effectively improves the universality and reliability of the method of this invention.

[0157] Preferably, the overflow rate of the molten metal filling and the volume of the mold cavity satisfy the following relationship:

[0158] In the formula, Overflow volume for molten filling; This refers to the volume of the mold cavity; The first proportionality constant has a value range of 0.1 to 0.2, and can be 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, and any value between them; The temperature difference between the first temperature and the second temperature. The second temperature; The speed at which molten liquid is injected into the mold cavity.

[0159] This invention derives the above-mentioned empirical model based on the thermodynamic and fluid dynamic mechanisms of the filling process. This model quantitatively describes the intrinsic relationship between the minimum theoretical overflow ratio required to obtain high-quality castings and the temperature difference between the molten metal and the mold, the absolute temperature level of the mold, and the speed at which the molten metal is injected into the mold cavity.

[0160] The core of the relationship proposed in this invention lies in determining the theoretical minimum overflow ratio related to process conditions. The value calculated on the right side of the formula represents the critical lower limit of the ratio of overflow to cavity volume that needs to be achieved under specific temperature differences, mold temperatures, and the rate at which molten metal is injected into the mold cavity, in order to ensure that the cold molten metal at the filling front and the entrained gas can be effectively discharged from the cavity, thereby obtaining a casting with a dense interior and intact surface.

[0161] Understandably, the use of a greater than or equal to relationship in the formula is to clearly define that, in the actual implementation of the method of this invention, the actual overflow ratio must be at least equal to or greater than the value calculated by this formula. As long as this condition is met, the most basic process requirement for cavity purification through overflow is achieved. This ensures that under different combinations of temperature differences, mold temperatures, and molten metal injection speeds into the mold cavity, the overflow rate dynamically meets the verified minimum standard. This invention does not impose an upper limit on the actual overflow ratio. Technically speaking, as long as the overflow system capacity of the mold allows, increasing the overflow rate generally will not damage but will only more thoroughly remove impurities. Therefore, the overflow ratio in actual production can be selected and optimized based on a trade-off between technical effectiveness and economic costs (metal loss, energy consumption).

[0162] Understandably, the constant in the relation This was determined through extensive repeatable die-casting tests under baseline and adjacent process conditions, and statistical analysis of the actual overflow ratio corresponding to the obtained high-quality castings. Under the premise of satisfying other core process conditions of this invention, By controlling the quality within this range, the goals of low porosity, no surface defects, and uniform microstructure can be achieved more stably.

[0163] Understandably, the temperature term in the relational expression adopts... The form of represents the physical significance of relative thermal shock intensity. Among them, molecules... Represents the driving force for heat exchange between the molten metal and the mold; the denominator The mold temperature level was introduced as a benchmark.

[0164] Understandably, overflow and temperature difference The direct correlation exists because a greater temperature difference results in a higher heat flux density at the moment of contact between the molten metal and the mold, a faster cooling rate at the solidification front, and a thicker layer of cold, viscous molten metal (which may be rich in oxides) formed per unit time. To effectively remove this increased cold molten metal from the casting body, a corresponding increase in the overflow rate for flushing and displacement is required. Overflow rate and the second temperature... The inverse relationship exists because mold temperature not only affects the temperature difference but also independently influences the flow behavior of the molten liquid. When the second temperature... At lower temperatures, even with temperature differences Similarly, the cooling effect of the mold on the molten metal is more pronounced. Low-temperature molds cause a rapid increase in the viscosity of the molten metal front, increasing flow resistance and thus increasing the force required to push the cold contaminant out. Furthermore, the lower secondary temperature... This means the mold's thermal capacity is at a low level, resulting in higher heat absorption efficiency and exacerbating the temperature drop at the molten front. Therefore, it implies that at the second temperature... Under lower operating conditions, the present invention requires a larger overflow to replenish the heat loss at the front edge with sufficient superheated melt, avoid incomplete filling, and provide stronger hydrodynamics to ensure the discharge of impurities.

[0165] Understandably, the reason for using the ratio of temperature difference to mold temperature is... Rather than a single parameter, this ratio constructs a dimensionless thermal index, taking into account temperature difference. Second temperature A single temperature difference cannot fully reflect the intensity of cooling, and the same temperature difference has different effects on the melt viscosity at different mold temperatures. By using a ratio, the formula can adaptively evaluate the actual cooling intensity under different mold temperature settings, thereby achieving precise matching of overflow.

[0166] Understandably, the exponent of the temperature term in the formula is 0.5 (square root), reflecting the nonlinear effect of the temperature difference on the rate of formation of the cold sludge at the solidification front. This aligns with the fundamental laws of heat conduction and solidification kinetics. According to Fourier's law of heat conduction and the theory of solidified layer growth, the thickness of the solidified shell or the cooling depth is usually proportional to the square root of the temperature difference. Since one of the main functions of the overflow is to displace the cold sludge layer formed during cooling, the required overflow volume is closely related to the thickness of this cold sludge layer. Given that the amount of cold sludge layer formed is related to the square root of the temperature difference, the proportion of overflow used for flushing should naturally also be positively correlated with the square root of the temperature difference. This exponent setting makes the formula more consistent with physical reality, avoiding overestimation or underestimation that might result from a linear relationship.

[0167] Understandably, the exponent of the second term in the equation is -1, reflecting another mechanism by which the speed of molten metal injection into the mold cavity affects the filling process and overflow requirements. When the speed of molten metal injection into the mold cavity decreases (i.e., filling slows down), the molten metal flow is more stable, and air entrapment within the cavity is significantly reduced, which is advantageous. However, slower filling also means a longer residence time of the molten metal in the cavity, increasing its overall heat loss, and potentially causing a more pronounced drop in the temperature of the molten metal at the leading edge. To maintain sufficient hydrodynamics during the longer filling time, pushing the potentially increased viscous resistance due to temperature drop and the continuously generated small amount of cold sludge at the leading edge towards and out of the overflow port, a sufficient molten metal flow rate is needed to provide continuous flushing. Therefore, the overflow ratio needs to be compensated for by a negative correlation with the speed of molten metal injection into the mold cavity; that is, the slower the filling, the larger the required minimum overflow ratio.

[0168] Understandably, the "2" in the second term of the relation is a normalization reference value, corresponding to... The characteristic process parameter value. The unit of "2" is m / s, which is taken from the upper limit of the velocity of the melt injection into the mold cavity of the present invention (≤2m / s), and is used as the normalization benchmark for this parameter, so that the term in the formula concerning the velocity of the melt injection into the mold cavity becomes a dimensionless factor.

[0169] Using this formula, those skilled in the art can calculate the required minimum overflow ratio based on specific process conditions. For example, when die-casting an aluminum alloy structural part, the process parameters are set as follows: Second temperature The melt temperature is 700℃, and the temperature difference between the melt and the mold is... The speed at which molten liquid is injected into the mold cavity Substitute the values ​​into the formula to calculate ( This yields a minimum a / b ratio of 0.15, meaning the minimum theoretical overflow ratio is approximately 0.15. The minimum total filling amount of the molten metal is approximately 115% of the cavity volume, which helps to obtain higher quality die-cast parts. If the second temperature is increased to... The temperature difference between the melt and the mold With other parameters remaining constant, the calculated minimum a / b ratio is approximately 0.13. This represents the ratio of temperature difference to mold temperature. As a relative indicator of thermal shock intensity, it can more accurately characterize overflow demand than a single temperature parameter. In actual production, the final overflow rate can be determined based on different calculation results and economic considerations.

[0170] In summary, this relationship links core thermodynamic parameters with fluid dynamic parameters, jointly determining the minimum process parameters required to achieve effective cavity purification. It replaces the traditional, crude experience-based approach of fixing the overflow ratio, achieving adaptive and scientific matching of overflow volume with specific process conditions. This dynamic control model reflects the systematic and precise nature of the invention's process, and is more conducive to the stable production of high-quality die-cast parts under a wide range of process parameter combinations.

[0171] Preferably, the molten filling overflow is discharged through an overflow port on the mold cavity; the overflow port is circumferentially disposed on the side wall of the mold cavity, and the area of ​​the overflow port accounts for 15% to 25% of the surface area of ​​the side wall of the mold cavity, which can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% and any value between them.

[0172] To better achieve the aforementioned overflow function, the overflow port design of this invention differs significantly in area from that of traditional die-casting processes. In the prior art, the main function of the overflow port is often understood as passively containing cold, contaminated metal and a small amount of gas; its total opening area is typically small, often accounting for less than 10% of the surface area of ​​the mold cavity sidewall. In contrast, this invention preferably requires the overflow port area to account for 15% to 25% of the surface area of ​​the mold cavity sidewall. This larger area percentage is more conducive to adapting to the core process of this invention.

[0173] Understandably, the overflow behavior in this invention is not a simple passive containment, but an active, quantitative flushing process. As mentioned above, this method controls the lower limit of the total overflow, and its lower limit (not less than 0.1) and its preferred implementation range are generally higher than the overflow of conventional processes. To accommodate this larger planned overflow, a preferred matching scheme is to provide it with an overflow channel with stronger flow capacity to ensure that at the end of the filling period, this portion of the melt rich in impurities and gases can be quickly, smoothly, and unimpededly discharged from the cavity, avoiding throttling or back pressure at the overflow port.

[0174] In this invention, the "area of ​​the overflow port" refers to the sum of the effective cross-sectional areas of the channels through which the molten liquid flows from inside the mold cavity to the external overflow system; the "surface area of ​​the sidewall of the mold cavity" refers to the actual total area of ​​the vertical or inclined surfaces around the mold cavity that form the product shape, excluding the bottom and top surfaces of the mold cavity (i.e., the plane where the parting surface is located). This invention controls the area of ​​the overflow port to account for 15% to 25% of the sidewall surface area of ​​the mold cavity, aiming to ensure that the flow capacity of the overflow system matches the cavity volume and heat dissipation surface area, thus meeting the requirements for rapid venting and slag removal under large overflow flow while ensuring the overall strength of the mold structure.

[0175] Specifically, this invention provides two typical mold structure implementation methods: The first embodiment is an independent overflow port structure, which can be a bi-splitting mold where the upper and lower mold mating surfaces are perpendicularly abutting. In this structure, the mold cavity is jointly enclosed by the upper and lower molds, and the outer walls of the upper and lower molds are usually set as vertical surfaces. When the mold is closed, the outer walls of the upper and lower molds abut each other perpendicularly to form a closed cavity sidewall. The overflow port is manifested as multiple independent through holes opened on the mold sidewall, preferably located in the upper region of the upper mold sidewall, so as to utilize the gas rising characteristics for venting. In this embodiment, the "area of ​​the overflow port" is the sum of the opening cross-sectional areas of each independent through hole at the inner wall of the cavity; the "surface area of ​​the mold cavity sidewall" corresponds to the total surface area of ​​the sidewalls of the cavity formed by the upper and lower molds after they are closed. Therefore, the area ratio in this embodiment refers to the ratio of the total cross-sectional area of ​​the independent overflow port through holes to the total surface area of ​​the cavity sidewalls formed by the upper and lower molds. This structure is easy to process and clean, and is suitable for castings with regular shapes and uniform overflow requirements.

[0176] The second implementation is a continuous overflow edge structure, which can be an insert-type mold with a vertical upper mold, an inclined lower mold, and the upper mold inserted into the lower mold. In this structure, the sidewall of the lower mold is designed as an inclined surface, and the sidewall of the upper mold is a vertical surface. When the mold is closed, the upper mold is inserted downward into the lower mold, and a fitting gap is formed between the end face of the upper mold and the inclined sidewall of the lower mold. At this time, the overflow port no longer appears as an independent through hole, but as a continuous overflow edge around the top of the lower mold (i.e., the fitting gap between the end face of the upper mold and the sidewall of the lower mold). After the molten metal is filled, the excess molten metal and gas overflow evenly from this ring gap at the top of the lower mold. In this implementation, the "area of ​​the overflow port" is the cross-sectional area of ​​the annular channel of the continuous overflow edge; the "surface area of ​​the mold cavity sidewall" mainly corresponds to the surface area of ​​the sidewall of the lower mold (because the main sidewall of the cavity is surrounded by the inclined surface of the lower mold, and the upper mold mainly forms the top). Therefore, the area ratio in this implementation refers to the ratio of the cross-sectional area of ​​the continuous overflow edge at the top of the lower mold to the surface area of ​​the sidewall of the lower mold cavity. This continuous overflow edge structure eliminates the dead zone between independent overflow ports, allowing the gas and cold molten sludge at the molten front to be discharged evenly and synchronously along the entire circumference of the cavity. It is particularly suitable for complex castings with extremely high requirements for airtightness and surface quality.

[0177] Regardless of the implementation method used, this invention controls the ratio of the overflow port area to the cavity sidewall surface area to be between 15% and 25%. For the first implementation method, if the ratio is below 15%, the total flow area of ​​the independent through holes is insufficient, which can easily lead to a throttling effect under large overflow flow processes, resulting in poor venting or back pressure at the overflow port. If the ratio is above 25%, the effective support area of ​​the upper and lower mold sidewalls decreases, weakening the mold strength and increasing the risk of mold expansion. For the second implementation method, if the ratio is below 15%, the gap between the continuous overflow edges is too narrow, which is not conducive to the smooth discharge of cold melt and can easily cause premature solidification and blockage of the overflow edges. If the ratio is above 25%, it means that the upper mold insertion depth is too shallow or the lower mold sidewall is too thin, which will also affect the guiding accuracy and structural rigidity of the mold. Therefore, the range of 15% to 25% is a balance point between fluid dynamics flow requirements and mold mechanical strength, which helps to ensure the stable implementation of the slow filling and large overflow process of this invention.

[0178] Step S106: Perform T6 heat treatment and anodizing on the die-cast aluminum alloy to obtain anodized die-cast aluminum alloy.

[0179] T6 heat treatment is a key step in obtaining high strength and a specific dual-mode strengthening phase distribution, while anodizing is an electrochemical process that generates a dense alumina film on the aluminum alloy surface. For the low-silicon 6-series die-cast aluminum alloy of this invention, due to its pure matrix and uniform structure, a high-quality oxide film can be obtained using an anodizing process similar to that used for high-quality rolled sheets.

[0180] Preferably, the T6 heat treatment includes: solution treatment at 520℃~540℃ for 1 hour to 4 hours, water quenching, and then aging treatment at 160℃~180℃ for 6 hours to 12 hours.

[0181] A solution temperature of 520℃~540℃ is sufficient for dissolving most of the Mg2Si phase in 6-series aluminum alloys, but below their overheating temperature to avoid grain boundary melting. A solution time of 1~4 hours ensures complete dissolution while also considering production efficiency. Water quenching is used for rapid cooling after solution treatment, preserving the supersaturated solid solution state from the high temperature to room temperature and preventing the precipitation of coarse equilibrium phases during cooling. An artificial aging temperature of 160℃~180℃ is typical for 6-series aluminum alloys, which is beneficial for forming a strengthening structure dominated by the β'' phase. An aging time of 6~12 hours ensures sufficient precipitation to reach peak strength. This invention aims to achieve a specific distribution of the aforementioned intermetallic compounds F and G through precise matching of solution and aging parameters: slightly lowering the solution temperature or shortening the solution time intentionally retains a small amount of undissolved coarse second phase as intermetallic compound F; while precise control of the aging temperature and duration determines the size, quantity, and distribution density of intermetallic compound G (fine β'' or β phase). These parameters, combined with specific alloy compositions and die-cast microstructures, are designed to simultaneously meet the requirements of high strength and uniform anodizing.

[0182] Furthermore, the die-cast microstructure obtained by the aforementioned die-casting process parameters (temperature difference control between molten metal and mold, low-speed stable filling, and large overflow design) provides an ideal matrix prerequisite for the precise precipitation of intermetallic compounds F and G during subsequent heat treatment. Specifically, the low silicon content and temperature difference control of 300℃~350℃ avoid excessive formation of primary silicon or coarse eutectic phases, resulting in a wide and gentle banded distribution of Mg and Si elements in a fine and uniform equiaxed matrix; the low-speed laminar flow filling and large overflow ratio effectively eliminate air entrapment and cold contamination at the leading edge, ensuring extremely high internal density and uniform solute distribution in the casting. Based on this highly homogeneous die-cast microstructure, a solution treatment at 520℃~540℃ allows Mg and Si elements to fully and uniformly dissolve back into the aluminum matrix to form a supersaturated solid solution. Simultaneously, only a very small amount of undissolved original grain boundary phase is retained as heterogeneous nucleation sites for the subsequent F phase. Subsequently, during aging at 160℃~180℃, the uniformly supersaturated matrix promotes the diffuse precipitation of numerous fine β'' / β phases (i.e., intermetallic compound G) in a needle-like morphology. The remaining grain boundary phases preferentially grow along the original grain boundaries and interconnect to form a continuous network structure (i.e., intermetallic compound F). The homogeneity and density of the die-cast microstructure directly determine the uniformity of the matrix composition after solution treatment, thereby precisely controlling the nucleation rate, growth kinetics, and final spatial distribution ratio of the F and G phases during aging. This ensures that the f / g value remains stably within the optimized range of 1.5~4, thus achieving a synergistic effect between high-strength support and electrochemical homogeneity of the anodized surface on a macroscopic scale.

[0183] Preferably, the anodizing treatment includes: in a sulfuric acid electrolyte with a concentration of 150 g / L to 200 g / L, at a temperature of 18°C ​​to 22°C, at an anode flow rate of 1.0 A / dm³.2 ~1.5A / dm 2 DC anodizing is performed at a current density of 20 to 40 minutes.

[0184] These process parameters are applicable to the low-silicon 6-series die-cast aluminum alloys of this invention. A sulfuric acid concentration of 150 g / L to 200 g / L provides sufficient sulfate ions to participate in the reaction, forming a porous oxide film, which is beneficial for subsequent coloring or sealing. An electrolyte temperature of 18°C ​​to 22°C is the ideal temperature range for obtaining a dense, hard, and uniform oxide film. Too low a temperature results in slow film formation and a hard but brittle film, while too high a temperature results in a loose film with low hardness. The current density is 1.0 A / dm³. 2 ~1.5A / dm 2 Matching the above temperature and concentration ensures that the oxide film grows at a moderate and controllable rate. An oxidation time of 20-40 minutes, combined with the above current density, can generate an oxide film of the target thickness. Because the matrix material provided by this invention is pure and has a uniform structure, a high-quality oxide film can be obtained using this standard sulfuric acid anodizing process without the need for special additives to the electrolyte or complex power waveforms, demonstrating the excellent adaptability of the material itself to anodizing. After oxidation, subsequent processing steps such as water washing, coloring (if necessary), and sealing are usually required; these are conventional techniques in the field.

[0185] Thirdly, the present invention provides an aluminum alloy die casting made of an anodized die casting aluminum alloy of the first aspect, or an anodized die casting aluminum alloy prepared by the preparation method of the second aspect.

[0186] The product of this invention is an aluminum alloy die-casting part, which is composed of the aforementioned anodized die-cast aluminum alloy material with specific composition, specific microstructure and specific surface characteristics, or produced by the aforementioned specific preparation method. This die-casting part inherits the advantages of the aluminum alloy of this invention, such as high strength, high density, and excellent anodized appearance. It can have various complex shapes, which is the advantage of near-net-shape forming in die-casting technology. For example, it can be a one-piece molded mobile phone frame, laptop shell, camera frame, drone parts, etc. These structural parts often have features such as reinforcing ribs, snap-fits, and threaded holes. Traditional sheet metal machining by CNC not only results in significant material waste, but also easily leads to color differences at the edges and corners during anodizing. The die-casting part of this invention can achieve one-piece molding of complex shapes with a uniform overall appearance.

[0187] Fourthly, the present invention provides an application of the aluminum alloy die-casting part as described in the third aspect in the manufacture of structural parts for electronic devices, transportation vehicles, robots, medical devices, industrial equipment, or new energy equipment.

[0188] Preferably, metal alloy die castings can be used in the manufacture of consumer electronics housings, precision automotive parts, humanoid robot mechanical components, or medical components.

[0189] The above are preferred application areas of the die-cast parts of this invention. These areas all have high requirements for material strength, lightweight, complex forming capabilities, and surface appearance. Applications in consumer electronics casings (such as the mid-frames and back panels of smartphones, tablets, laptops, and smartwatches) are a key scenario. These products require thin yet robust casings that protect internal precision components, while their appearance (color, gloss, texture) is a crucial factor in determining product quality and consumer perception. The die-cast parts of this invention perfectly meet these needs. The 6-series aluminum alloy provides high strength, enabling thinner wall designs; die casting allows for integrated molding of complex structures, reducing assembly parts; and excellent anodizing properties provide a uniform color and smooth surface comparable to or even better than sheet aluminum. Applications in automotive precision parts, such as structural supports, chassis components, trim strips, and battery pack housings, also benefit from their high strength, lightweight, good corrosion resistance, and consistent appearance. In humanoid robot mechanical components (such as joint connectors, skeletons, and shells), lightweight, high-strength, wear-resistant, and fatigue-resistant materials are required. The die-casting parts of this invention, through T6 heat treatment, can achieve high mechanical properties, meeting the needs of such dynamic load-bearing components. In medical components (such as medical device shells, stents, and non-implantable tools), there are requirements for the biocompatibility of materials (usually requiring low-toxicity metals), surface cleanliness, and disinfection resistance. Aluminum alloy anodized films have good chemical stability and a clean surface, and the high-purity, high-density die-casting parts of this invention provide the means for this. These examples illustrate the broad market prospects and industrialization value of the technical solution of this invention. Through material and process innovation, die casting, a high-efficiency, low-cost forming technology, can directly produce structural parts that meet the appearance and performance requirements of the high-end market. It is expected to replace some of the complex processing paths of traditional forging + CNC + anodizing or rolled sheet + CNC + anodizing, bringing significant cost and efficiency advantages.

[0190] The present invention will be further described in detail below with reference to specific embodiments, but these are exemplary and do not limit the scope of protection of the present invention in any way.

[0191] Example 1 An anodized die-cast aluminum alloy is prepared by the following method: Step S102: Weigh the raw materials according to the following mass percentages: Si content 0.7%, Mg content 1.0%, Ti content 0.12%, other unavoidable impurities (Fe, Cu, etc.) ≤0.15%, and the balance is Al. After melting, a molten liquid is formed. The temperature of the molten liquid (first temperature) is controlled at 700℃ and held at this temperature. The mold cavity is preheated to 380℃ (second temperature) and held at this temperature, with a temperature difference ΔT of 320℃.

[0192] Step S104: The molten liquid is injected into the mold cavity through the inlet of the mold cavity. The speed at which the molten liquid is injected into the mold cavity is 1.0 m / s, and the moving speed of the molten liquid surface in the mold cavity relative to the mold cavity is 0.3 m / s. After the cavity is filled, pressure is maintained and the mold is opened to obtain the die-cast aluminum alloy.

[0193] Among them, the cross-sectional area of ​​the flow channel changes 0 between the position where the liquid inlet contacts the mold cavity and the position where it is far away from the mold cavity; The ratio of the overflow volume of the molten filling to the volume of the mold cavity is 0.2; the overflowing molten filling is discharged through the overflow port on the mold cavity; the area of ​​the overflow port accounts for 20% of the side wall surface area of ​​the mold cavity, and the overflow port is a continuous overflow edge structure, which is set along the circumference of the top of the lower mold.

[0194] Step S106: Perform T6 heat treatment on the die-cast aluminum alloy: solution treatment at 530℃ for 2 hours, followed by water quenching; then age treatment at 170℃ for 8 hours.

[0195] Anodizing was then performed: in a sulfuric acid electrolyte with a concentration of 180 g / L, at 20 °C, at a rate of 1.2 A / dm³. 2 DC anodizing was performed at a certain current density for 30 minutes, followed by water washing and sealing to obtain anodized die-cast aluminum alloy products.

[0196] Example 2 The preparation method of this embodiment is the same as that of Example 1, except that the Si content in the aluminum alloy is 1.0%.

[0197] Example 3 The preparation method of this embodiment is the same as that of Example 1, except that the Si content in the aluminum alloy is 0.3%.

[0198] Example 4 The preparation method in this embodiment is the same as that in Example 1, except that Ti element is not actively added to the aluminum alloy composition and the Ti content is 0.

[0199] Example 5 The preparation method of this embodiment is the same as that of Example 1, except that the Ti content in the aluminum alloy is 0.01%.

[0200] Example 6 The preparation method in this embodiment is the same as that in Example 1, except that the Ti content in the aluminum alloy is 0.20%.

[0201] Example 7 The preparation method of this embodiment is the same as that of Example 1, except that the Mg content in the aluminum alloy is 0.4%.

[0202] Example 8 The preparation method in this embodiment is the same as that in Example 1, except that the Mg content in the aluminum alloy is 1.5%.

[0203] Example 9 The preparation method in this embodiment is the same as that in Example 1, except that the melt temperature is 680°C, the mold cavity temperature is 380°C, and the temperature difference is 300°C.

[0204] Example 10 The preparation method in this embodiment is the same as that in Example 1, except that the melt temperature is 720°C, the mold cavity temperature is 370°C, and the temperature difference is 350°C.

[0205] Example 11 The preparation method in this embodiment is the same as that in embodiment 1, except that: the molten liquid is filled into the mold cavity through the inlet of the mold cavity at a speed of 0.3 m / s, and the moving speed of the molten liquid surface in the mold cavity relative to the mold cavity is 0.15 m / s.

[0206] Example 12 The preparation method in this embodiment is the same as that in embodiment 1, except that: the molten liquid is filled into the mold cavity through the inlet of the mold cavity at a speed of 0.5 m / s, and the moving speed of the molten liquid surface in the mold cavity relative to the mold cavity is 0.25 m / s.

[0207] Example 13 The preparation method in this embodiment is the same as that in embodiment 1, except that: the molten liquid is filled into the mold cavity through the inlet of the mold cavity at a speed of 2 m / s, and the moving speed of the molten liquid surface in the mold cavity relative to the mold cavity is 0.5 m / s.

[0208] Example 14 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the cross-sectional area of ​​the flow channel changes by -10% between the position where the liquid inlet contacts the mold cavity and the position where it is far away from the mold cavity.

[0209] Example 15 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the cross-sectional area of ​​the flow channel changes by -5% between the position where the liquid inlet contacts the mold cavity and the position where it is far away from the mold cavity.

[0210] Example 16 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the cross-sectional area of ​​the flow channel changes by +5% between the position where the liquid inlet contacts the mold cavity and the position where it is far away from the mold cavity.

[0211] Example 17 The die-casting method in this embodiment is the same as that in Embodiment 1, except that the cross-sectional area of ​​the flow channel changes by +10% between the position where the liquid inlet contacts the mold cavity and the position where it is far away from the mold cavity.

[0212] Example 18 The preparation method of this embodiment is the same as that of Example 1, except that the solution temperature of the T6 heat treatment is 520°C, the solution time is 4 hours, the aging temperature is 160°C, and the aging time is 12 hours.

[0213] Example 19 The preparation method of this embodiment is the same as that of Example 1, except that: the solution temperature of T6 heat treatment is 540℃, the solution time is 1 hour, the aging temperature is 180℃, and the aging time is 6 hours.

[0214] Example 20 The preparation method in this embodiment is the same as in Example 1, except that: the anodic oxidation treatment is carried out in a sulfuric acid electrolyte with a concentration of 150 g / L at a temperature of 18°C ​​and an anode flow rate of 1.0 A / dm³. 2 The oxidation was carried out at a current density of 40 minutes.

[0215] Example 21 The preparation method in this embodiment is the same as in Example 1, except that: the anodic oxidation treatment is carried out in a sulfuric acid electrolyte with a concentration of 200 g / L at a temperature of 22°C and an anode flow rate of 1.5 A / dm³. 2 The oxidation was carried out at a current density of 20 minutes.

[0216] Example 22 The preparation method in this embodiment is the same as that in Example 1, except that the ratio of the overflow of the melt filling to the volume of the mold cavity is 0.1.

[0217] Example 23 The preparation method in this embodiment is the same as that in Example 1, except that the ratio of the overflow of the melt filling to the volume of the mold cavity is 0.5.

[0218] Example 24 The preparation method in this embodiment is the same as that in Example 1, except that the ratio of the overflow of the melt filling to the volume of the mold cavity is 0.6.

[0219] Example 25 The preparation method in this embodiment is the same as in Example 1, except that the ratio of the overflow rate of the melt filling to the volume of the mold cavity is determined by calculation using a formula:

[0220] Among them, take Temperature difference between melt and mold Second temperature The speed at which molten liquid is injected into the mold cavity The calculated ratio is approximately 0.18.

[0221] Example 26 The preparation method of this embodiment is the same as that of embodiment 1, except that the area of ​​the overflow port accounts for 25% of the side wall surface area of ​​the mold cavity.

[0222] Example 27 The preparation method of this embodiment is the same as that of embodiment 1, except that the area of ​​the overflow port accounts for 15% of the side wall surface area of ​​the mold cavity.

[0223] Example 28 The preparation method of this embodiment is the same as that of embodiment 1. The difference is that the overflow port is an independent overflow port structure. Specifically, an overflow port is provided on the upper part of each side wall of the mold cavity. The overflow port is circular in shape and the area of ​​the overflow port accounts for 20% of the surface area of ​​the side wall of the mold cavity.

[0224] Comparative Example 1 This comparative example provides a conventional 6-series die-cast aluminum alloy with the following composition by mass percentage: 5.0% Si, 0.6% Mg, 0.2% Fe, and the balance Al (close to the composition of high-silicon die-casting alloys such as ADC12). The melt temperature is 700℃, the mold temperature is 200℃, and the temperature difference is 500℃. The melt injection rate is 4.0 m / s, and a conventional gating design (cross-sectional area shrinkage >90%) is used. Subsequent T6 heat treatment is not performed; instead, the same anodizing treatment as in Example 1 is applied directly.

[0225] Comparative Example 2 The preparation method of this comparative example is the same as that of Example 1, except that the speed at which the melt is injected into the mold cavity is 4.0 m / s, the speed at which the melt surface moves within the mold cavity is 2.0 m / s, and other parameters are the same as those of Example 1.

[0226] Comparative Example 3 The preparation method of this comparative example is the same as that of Example 1, except that: the melt holding temperature is 720°C, the mold cavity holding temperature is 200°C, the temperature difference is 520°C, and other parameters are the same as those of Example 1.

[0227] Comparative Example 4 The preparation method of this comparative example is the same as that of Example 1, except that the cross-sectional area shrinkage rate of the flow channel at the inlet reaches 90%, resulting in a velocity of 5m / s when the melt enters the cavity. Other parameters are the same as those of Example 1.

[0228] Comparative Example 5 The preparation method of this comparative example is the same as that of Example 1, except that the die-cast aluminum alloy is directly subjected to the same anodizing treatment as in Example 1, without undergoing T6 heat treatment.

[0229] Comparative Example 6 The preparation method of this comparative example is the same as that of Example 1, except that the T6 heat treatment solution temperature is 480℃, the solution time is 0.5 hours, and other parameters are the same as those of Example 1.

[0230] Comparative Example 7 The preparation method of this comparative example is the same as that of Example 1, except that the aging temperature of T6 heat treatment is 200℃ and the aging time is 24 hours, while other parameters are the same as those of Example 1.

[0231] Comparative Example 8 The preparation method of this comparative example is the same as that of Example 1, except that the ratio of the overflow of the first filling and the second filling to the volume of the mold cavity is 0.05.

[0232] Test case The following performance tests were performed on the aluminum alloys obtained in all embodiments and comparative examples: 1. Microstructure analysis in the die-cast state: Grain size: After grinding, polishing and etching (Keller's reagent) of the die-cast sample, the average grain size and standard deviation of at least 5 fields of view were statistically analyzed using a metallographic microscope (500X) and image analysis software (according to ASTM E112 standard).

[0233] Pore ​​analysis: Ten 500 μm pores were randomly selected from the above metallographic samples. 2 The field of view was used to identify and statistically analyze areas ≥10μm using image analysis software. 2 The number of pores is determined, and their average value is calculated.

[0234] 2. Analysis of the T6 state strengthening phase: The samples after T6 heat treatment were ground, polished, and etched (using a mixed acid solution). They were then observed using a field emission scanning electron microscope (FESEM) in backscattered electron mode.

[0235] Using image analysis software, at least 5 different fields of view (each field of view area ≥ 500 μm) were analyzed. 2 In the study, the area ratio f of intermetallic compound F with equivalent circle diameter of 3μm-6μm and the area ratio g of intermetallic compound G with equivalent circle diameter of 0.03μm-3μm are distinguished and statistically analyzed, and the f / g value is calculated.

[0236] 3. Characterization of anodic oxide film: Film thickness: The thickness was measured at multiple points on the sample surface using an eddy current thickness gauge, and the average value was taken.

[0237] Surface morphology: The arithmetic mean height Sa and the average width Rsm of the contour unit on the surface of the anodic oxide film were measured using a white light interferometer. The average value was taken after 5 measurements.

[0238] Color: The L*, a*, and b* values ​​of the central region of the sample surface were measured using a standard spectrophotometer (D65 light source, 10° field of view).

[0239] Occurrence rate of appearance defects: Visually inspect the surface of the anodized sample and count the proportion of the area with any visible defects (color difference, bright spots, dark lines, water flow lines, etc.) to the total surface area, and take the average value.

[0240] 4. Grain boundary composition distribution analysis: Electron probe microanalysis (EPMA) was used to perform line scan tests on the die-cast specimens. On the polished and etched metallographic specimens, a line scan with a length of at least 0.3 mm was performed parallel to the alloy width direction and spanning multiple grains, with a step size of 5 μm, to obtain the concentration distribution curve of Mg. A continuous interval with a concentration variation less than 0.03% by mass was defined as a "band." This band is a macroscopic compositional band formed by the arrangement and connection of solute segregation regions at multiple grain boundaries. The concentration jump value between adjacent bands is the concentration difference, and the projected length of the macroscopic compositional band in the alloy width direction is the band width.

[0241] 5. Freezing point test: The solidification point of the alloy was determined by differential scanning calorimetry (DSC). Approximately 50 mg of sample was taken and cooled from 700 °C to 400 °C at a cooling rate of 10 °C / min under argon protection. The exothermic curve was recorded, and the onset temperature of the exothermic peak was taken as the solidification point.

[0242] Based on the above testing methods, the examples and comparative examples were tested, and the resulting performance data are summarized in Table 1.

[0243] Table 1

[0244] As shown in Table 1, comprehensive performance tests were conducted on the anodized die-cast aluminum alloys prepared in each embodiment and comparative example of the present invention. The test results clearly verify the effectiveness of the technical solution of the present invention. As can be seen from the data in Table 1, the aluminum alloys prepared in the embodiments all meet the requirements of the present invention in terms of microstructure parameters and anodizing performance indicators. Within the specified range of parameters, the alloys in the embodiments can obtain good microstructure uniformity and anodized appearance quality, proving the rationality of the process parameter ranges set in the present invention. In contrast, the comparative examples, due to deviation from the process conditions of the technical solution of the present invention, show a significant deterioration in all performance indicators. In summary, the data in Table 1 fully demonstrates that the present invention, through the combined effect of low-silicon composition design, precise microstructure control, and synergistic optimization of process parameters, enables 6-series die-cast aluminum alloys to achieve a significant improvement in anodized appearance quality while maintaining good mechanical properties. The appearance quality is close to that of rolled sheet metal, effectively solving the technical bottleneck of the prior art where the die-casting formability and anodizing performance of 6-series aluminum alloys are difficult to balance.

[0245] To further demonstrate the technical effectiveness of the present invention, the following analysis will be conducted in conjunction with specific experimental test results and images.

[0246] Figure 1 The image shows the metallographic structure of an aluminum alloy sample after T6 heat treatment according to Example 1 of this invention. The distribution characteristics of two Mg2Si strengthening phases with different sizes and morphologies can be observed in the image. The specific locations of intermetallic compounds F and G are clearly indicated by arrows and text labels in the image. The black network structure represents intermetallic compound F (as shown by the arrows and network labels in the image), with an equivalent circle diameter of approximately 3 μm to 6 μm, forming a continuous network framework along grain boundaries or subgrain boundaries, with an area fraction f of approximately 1.5%. Within the mesh of the network structure, finer needle-like or dot-like precipitates, i.e., intermetallic compound G (as shown by the arrows and needle labels in the image), are dispersed, with an equivalent circle diameter of approximately 0.03 μm to 3 μm, an area fraction g of approximately 0.6%, and an f / g ratio of approximately 2.5. The continuous network F phase provides good grain boundary pinning and structural support, while the fine, dispersed G phase achieves efficient precipitation strengthening. Under the process conditions of Example 1, the melt solidification process was stable and the grain size was uniform, providing ideal matrix conditions for the preferential precipitation of the strengthening phase after T6 heat treatment. The strengthening phase is uniformly distributed in the figure, without local enrichment or depletion. The area ratio of the F phase to the G phase is within the preferred range defined by this invention, directly corresponding to the excellent appearance quality of the surface after anodizing, which has no visible defects. This demonstrates the success of the synergistic control of the composition design and process parameters in this invention.

[0247] Figure 2This is a metallographic image of the aluminum alloy in the die-cast state according to Example 1 of the present invention. As can be observed from the image, the microstructure exhibits uniform and fine equiaxed grain characteristics, with an average grain size of approximately 20 μm and a standard deviation of approximately 10 μm. The grain size distribution is concentrated, with no obvious coarse dendrites or columnar crystal regions. No areas ≥10 μm are observed within the field of view. 2 The macroscopic porosity meets the requirements of this invention. In this embodiment, the low silicon content reduces coarse segregation of the eutectic phase, the addition of trace amounts of Ti provides an effective heterogeneous nucleation core, the temperature difference between the melt and the mold is controlled within the range of 300℃~350℃ to avoid surface defects caused by rapid cooling, the low-speed filling eliminates turbulent air entrapment, the gateless and gentle flow channel design ensures smooth melt introduction, and the appropriate overflow ratio ensures effective discharge of the cold melt at the leading edge. This die-cast microstructure provides a uniform solute distribution basis for subsequent T6 heat treatment, ensuring the appearance quality of the final product.

[0248] Figure 3 This image shows the metallographic structure of an aluminum alloy sample after T6 heat treatment, as described in Example 11 of this invention. Example 11 employed extremely low melt injection and surface movement speeds. The intermetallic compound F and intermetallic compound G are clearly distinguished in the image using arrows and text labels. It can be observed that the area fraction f of intermetallic compound F is approximately 1.6%, while the area fraction g of intermetallic compound G is approximately 0.55%, with an f / g ratio of approximately 2.9. The extremely low filling speed significantly reduces melt turbulence, resulting in a more uniform distribution of solute elements and an increased and more dispersed nucleation rate of precipitated phases. This microstructure characteristic contributes to the formation of an extremely low arithmetic mean oxide film height Sa and a low incidence of surface defects, verifying the positive effect of the low-speed filling process on further improving surface quality.

[0249] Figure 4 This is a metallographic image of the aluminum alloy in the die-cast state according to Example 11 of the present invention. As can be observed from the image, the microstructure exhibits highly uniform fine equiaxed crystals, with no crystals ≥10 μm in size within the field of view. 2 The microstructure exhibits zero macroscopic porosity. Thanks to the synergistic effect of slow, stable filling and large overflow, the cold contaminant layer at the molten front is effectively expelled, and air entrapment defects are extremely well controlled. The high density of this die-cast microstructure provides a uniform matrix for subsequent T6 heat treatment, ensuring the integrity and uniformity of the final anodized film.

[0250] Figure 5This is a photograph of the anodized appearance of an aluminum alloy die-casting part made of aluminum alloy according to Embodiment 1 of the present invention. As can be clearly seen from the image, the surface of the die-casting part has a uniform and consistent color, exhibiting a gray metallic texture, without any visible defects such as runout lines, black streaks, bright spots, or color differences. The surface has a soft luster without glare, demonstrating the excellent anodizing performance achieved by the aluminum alloy of the present invention under precise control of low silicon content and microstructure. The appearance quality is close to or even reaches the level of rolled sheet metal.

[0251] Figure 6 This is a photograph of the anodized appearance of the aluminum alloy die-casting part made of aluminum alloy, Comparative Example 2 of this invention. Comparative Example 2 uses a conventional high-speed die-casting process. It can be clearly observed from the image that the surface exhibits severe flow lines and color differences, uneven gloss in localized areas, and a high incidence of appearance defects. This is because high-speed filling leads to severe melt turbulence, entraining gas and forming oxide inclusions. Furthermore, the coarse grains and numerous pores result in inconsistent electrochemical responses during the anodizing process. Figure 5 and Figure 6 The stark contrast powerfully demonstrates the remarkable technical effectiveness of the low-speed, stable filling process of this invention in eliminating appearance defects.

[0252] Figure 7 and Figure 8 The diagrams show a comparison between the gateless structure of this invention and the narrow gate structure of the prior art. For example... Figure 7 As shown, in this invention, the change in the cross-sectional area of ​​the flow channel between the inlet 20 and the injection mechanism 40 is controlled within ±10%. After the molten liquid is output from the injection mechanism 40, it directly enters the mold cavity 10 through the smooth flow channel, without any throttling parts with abrupt cross-sectional contraction. This gateless design ensures that the flow velocity of the molten liquid in the flow channel will not undergo abrupt forced acceleration, and the movement speed of the injection punch can be transmitted to the cavity in a highly linear manner, providing a structural basis for achieving low-speed laminar flow filling. In contrast, as... Figure 8 As shown, in traditional narrow gate structures, the cross-sectional area at the inlet 20 is deliberately designed to be 3% to 9% of the cross-sectional area of ​​the upstream flow channel. When the molten liquid flows through this part, it will be uncontrollably accelerated to a high-speed jet state (usually >2m / s), generating strong turbulence and air entrapment. This is the structural root cause of surface defects and internal porosity in traditional die castings. Figure 7 and Figure 8 The comparison clearly reveals the technical principle of this invention in eliminating turbulence-inducing factors from the structural source.

[0253] Figure 9 and Figure 10 The specific embodiments of the continuous overflow edge structure in the mold of the present invention are shown from both a three-dimensional perspective and a side view. For example... Figure 9 and Figure 10As shown, the overflow port 30 is not a traditional independent through hole, but a continuous annular channel set on the top side of the lower mold. Multiple overflow ports 30 are connected around the circumference of the mold cavity 10 to form a complete overflow edge. When the upper and lower molds are closed, this continuous overflow edge cooperates with the upper mold to form a complete venting and slag removal channel around the top of the cavity. The advantages of this structural design are: First, it eliminates the venting dead angle that may exist between independent overflow ports, allowing the gas and cold molten sludge at the front of the molten metal to be discharged evenly and synchronously along the entire circumference of the cavity; Second, the overflow stalk formed on the casting by the continuous overflow edge is complete and continuous, which is convenient for subsequent one-time removal by special tooling, improving post-processing efficiency; Third, the large cross-sectional area of ​​the overflow edge ensures that the flow rate of the molten metal through the overflow port 30 can still be kept at a low level under high overflow flow process, maintaining a laminar or steady flow state, and achieving truly stable rinsing.

[0254] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An anodized die-cast aluminum alloy, characterized in that, The anodized die-cast aluminum alloy comprises the following elements by weight percentage: 0.3%~1.0% Si, 0.4%~1.5% Mg, the total content of unavoidable impurities is no more than 0.3%, and the balance is Al; Before heat treatment, the aluminum alloy has an average grain size of 10μm to 30μm, and the standard deviation of the grain size is no greater than 30μm; in any 500μm of the aluminum alloy 2 Within the observation area, the area is not less than 10 μm 2 The number of pores is no more than 1.

2. The anodized die-cast aluminum alloy according to claim 1, characterized in that, Before heat treatment, the aluminum alloy is subjected to any 500μm of heat treatment. 2 Within the observation area, there is no area not less than 10 μm 2 pores.

3. The anodized die-cast aluminum alloy according to claim 1, characterized in that, Before heat treatment, the solid solution concentration of Mg at the grain boundaries of the aluminum alloy varies in a banded pattern with a width of more than 0.1 mm along the width direction of the alloy, and the concentration difference between adjacent bands is less than 0.15% by mass.

4. The anodized die-cast aluminum alloy according to claim 1, characterized in that, After heat treatment, the aluminum alloy contains two Mg2Si intermetallic compounds, F and G, wherein the equivalent circle diameter of intermetallic compound F is 3μm~6μm and the equivalent circle diameter of intermetallic compound G is 0.03μm~3μm; in any observation region of the aluminum alloy, the ratio (f / g) of the area ratio f of intermetallic compound F to the area ratio g of intermetallic compound G is 1.5~4.

5. The anodized die-cast aluminum alloy according to claim 4, characterized in that, In any observation region of the aluminum alloy, the sum of the area ratio f of intermetallic compound F and the area ratio g of intermetallic compound G is not less than 1.5%.

6. The anodized die-cast aluminum alloy according to claim 4, characterized in that, The intermetallic compound F is in a continuous network morphology, and the intermetallic compound G is in a needle-like morphology.

7. The anodized die-cast aluminum alloy according to claim 4, characterized in that, The dispersion density of the Mg2Si intermetallic compound is 10 particles / μm. 2 ~200 cells / μm 2 .

8. The anodized die-cast aluminum alloy according to claim 1, characterized in that, After anodizing, the aluminum alloy has an anodized film on its surface, and the arithmetic mean height Sa of the anodized film is 0.1μm~0.5μm, and the average width Rsm of the contour unit is 0.5μm~10μm.

9. The anodized die-cast aluminum alloy according to claim 1, characterized in that, The surface color of the anodized die-cast aluminum alloy has a* < 0.1, b* < 1.0, and L* < 25.

10. The anodized die-cast aluminum alloy according to claim 8, characterized in that, The incidence of surface defects in the anodic oxide film is less than 0.05%.

11. The anodized die-cast aluminum alloy according to claim 1, characterized in that, The anodized die-cast aluminum alloy comprises 0.6% to 0.8% Si by weight percentage.

12. The anodized die-cast aluminum alloy according to claim 1, characterized in that, The anodized die-cast aluminum alloy further comprises 0.01% to 0.2% Ti by weight percentage.

13. The anodized die-cast aluminum alloy according to claim 12, characterized in that, The anodized die-cast aluminum alloy further comprises 0.1% to 0.15% Ti by weight percentage.

14. The anodized die-cast aluminum alloy according to claim 1, characterized in that, The solidification point range of the anodized die-cast aluminum alloy is 570℃~620℃.

15. The anodized die-cast aluminum alloy according to claim 1, characterized in that, The heat treatment includes T4, T5, T6 or T651 heat treatment.

16. A method for preparing anodized die-cast aluminum alloy as described in any one of claims 1 to 15, characterized in that, Includes the following steps: Step S102: The metal alloy is melted to form a molten liquid. The molten liquid includes the following elements by mass percentage: 0.3%~1.0% Si, 0.4%~1.5% Mg, the total content of unavoidable impurities is not greater than 0.3%, and the balance is Al. The molten liquid is kept at a first temperature, and the mold is kept at a second temperature lower than the first temperature. The temperature difference between the first and second temperatures is 300℃~350℃. Step S104: The molten liquid is injected into the mold cavity through the inlet of the mold cavity. After the mold cavity is filled, pressure is maintained and the mold is opened to obtain the die-cast aluminum alloy. The speed at which the molten liquid is injected into the mold cavity is no greater than 2 m / s, and the moving speed of the molten liquid surface relative to the mold cavity is no greater than 0.5 m / s; The cross-sectional area of ​​the flow channel varies within ±10% between the position where the liquid inlet contacts the mold cavity and the position where it is far away from the mold cavity. The ratio between the overflow rate of the molten filling and the volume of the mold cavity is not less than 0.1; Step S106: Perform heat treatment and anodizing on the die-cast aluminum alloy to obtain the anodized die-cast aluminum alloy.

17. The preparation method according to claim 16, characterized in that, The ratio between the overflow rate of the molten filling and the volume of the mold cavity is in the range of 0.1 to 0.

5.

18. The preparation method according to claim 16, characterized in that, The overflow rate of the molten metal and the volume of the mold cavity satisfy the following relationship: In the formula, Overflow volume for molten filling; This refers to the volume of the mold cavity; This is the first proportionality constant, and its value ranges from 0.1 to 0.2; The temperature difference between the first temperature and the second temperature. The second temperature; The speed at which molten liquid is injected into the mold cavity.

19. The preparation method according to claim 16, characterized in that, The molten filling overflow is discharged through the overflow port on the mold cavity; the overflow port is arranged circumferentially on the side wall of the mold cavity, and the area of ​​the overflow port accounts for 15% to 25% of the surface area of ​​the side wall of the mold cavity.

20. The preparation method according to claim 16, characterized in that, The heat treatment is T6 heat treatment, and the specific steps include: solution treatment at 520℃~540℃ for 1 hour to 4 hours, water quenching, and then aging treatment at 160℃~180℃ for 6 hours to 12 hours.

21. The preparation method according to claim 16, characterized in that, The anodizing treatment includes: in a sulfuric acid electrolyte with a concentration of 150 g / L to 200 g / L, at a temperature of 18°C ​​to 22°C, at an A / dm³... 2 ~1.5A / dm 2 DC anodizing is performed at a current density of 20 to 40 minutes.

22. An aluminum alloy die-casting part, characterized in that, Made of anodized die-cast aluminum alloy according to any one of claims 1 to 15, or anodized die-cast aluminum alloy prepared by any one of claims 16 to 21.

23. The application of the aluminum alloy die-casting part as described in claim 22 in the manufacture of structural parts for electronic devices, transportation vehicles, robots, medical devices, industrial equipment, or new energy equipment.

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